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The Acadian epoch is an epoch at the beginning of the American Palaeozoic time, and includes the oldest American rocks known to be fossiliferous.
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Acanthite is a mineral very similar to argentite, differing only in internal structure; the crystal of Acanthite being monoclinic - acanthite can be turned into argentite by heating. Acanthite is an important ore of silver, and forms spiky-looking crystals.
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In mineralogy, the term 'accessory' refers to a mineral that occurs in a rock in minute quantities, and does not affect the way the rock is named or classified.;
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Acicular refers to an external shape that resembles a needle.
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The term acidic rock refers to an igneous rock that consists mostly of light coloured minerals and has more than 66% free or combined silica.
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Acrotomous is a term describing a rock that has a cleavage parallel with the base.
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Actinolite is a mineral that commonly occurs in crystalline schists, often being the chief constituent of green-coloured schists and greenstones. It is used somewhat as an asbestos material. It has the formulae Ca2(Mg,Fe)5Si8O22(OH)2 (the same as nephrite, but being less attractive and harder to cut and polish is less valuable than nephrite) and a relative hardness of 6.
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Adamantine refers to a brilliant lustre like that of a diamond (adamant). It results from a mineral having a high index of refraction.
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Adamantine spar is an old name for the mineral corundum or of a brownish variety of it.
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Adamite is a rare mineral with a brilliant fluorescence, it is of scientific interest and is much desired by collectors for its bright colours and general attractiveness, but has no industrial use. It has the formulae Zn2(AsO4)(OH) and a relative hardness of 4. Adamite was discovered by the French mineralogist Gilbert-Joseph Adam at Chanarcillo, Chile during the 19th century, and the mineral was confirmed as a distinct species in 1886 and named after its discoverer.
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In geology, adobe are alluvial and playa clays of desert and arid regions, differing from ordinary clays of humid regions in containing carbonates and other soluble minerals.
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Adularia (Moonstone) is a semi-precious, clear, transparent, glassy form of potash feldspar which is found mainly in the crevices of crystalline schists and gneisses, often in beautifully perfect crystals. It has sometimes a pearly, opalescent reflection or play of colours. It derives its name from Adula, a mountain peak in Switzerland, where fine specimens are found.
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Aegirite (Aegirine) is a rock-forming mineral of the pyroxenes group, distinguished by it's long needle-like crystals, found mainly in rocks rich in soda and poor in silica. Named after Aegir, Icelandic god of the sea. It has the formulae NaFe(Si2O6) and a relative hardness of 7.
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Agalmatolite is a soft species of mineral of a greyish, greenish, or yellowish colour, also called pagodite and figure-stone, used by the Chinese for carving, especially into grotesque figures.
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Agaric Mineral or mountain-meal is one of the purest of the native carbonates of lime. It is found chiefly in the clefts of rocks and at the bottom of some lakes in a loose or semi-indurated form resembling a fungus. The name is also applied to a stone of loose consistence found in Tuscany, of which bricks may be made so light as to float in water, and of which the ancients are supposed to have made their floating bricks. It is a hydrated silicate of magnesium, mixed with lime, alumina, and a small quantity of iron.
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Agate is a semi-precious stone siliceous semi-pellucid compound mineral, consisting of bands or layers of various colours blended together, the base generally being chalcedony, and this mixed with variable proportions of jasper, amethyst, quartz, opal, heliotrope, and carnelian. The varying manner in which these materials are arranged causes the agate when polished to assume some characteristic appearances, and thus certain varieties are distinguished, as the ribbon agate, the fortification agate, the zone agate, the star agate, the moss agate, the clouded agate, etc. In Scotland they are cut and polished under the name of Scottish pebbles.
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In geology, agglomerate is a collective name for masses consisting of angular fragments ejected from volcanoes. When a rock mass consists largely of fragments worn and rounded by water it is called a conglomerate, and such masses were originally, no doubt, gravels and shingles on sea beaches and river channels.
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In geology, aggregate is a term applied to rocks composed of several different mineral constituents capable of being separated by mechanical means, such as granite, where the quartz, feldspar, and mica can be separated mechanically.
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The Alabama period is a period in the American Eocene, the lowest in the tertiary age except for the Lignitic.
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Since the Middle Ages the term alabaster has been applied to a compact variety or sulphate of lime, or gypsum, of a fine texture, and usually white and translucent, but sometimes yellow, red, or grey. It is carved into vases, mantel ornaments, etc. In ancient times the term alabaster was applied to a hard, compact variety of carbonate of lime (onyx), somewhat translucent, or of banded shades of colour. A variety of carbonate of lime, closely resembling alabaster in appearance, is used for similar purposes under the name of Oriental alabaster. It is usually stalagmitic or stalactitic in origin and is often of a yellowish colour. It may be distinguished from true alabaster by being too hard to be scratched with the nail.
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Albertite is a bituminous mineral resembling asphalt found in the county of Albertite, New Brunswick.
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Albite or soda-feldspar is a widely distributed, rock-forming mineral present in pegmatite dikes and may be found in crystals. It has the formulae NaAlSi3O8 and a relative hardness of 7. Albite is a form of feldspar, and is usually white in colour, hence its name, but is occasionally bluish, grayish, greenish, or reddish white.
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Alexandrite is a variety of chrysoberyl found in the mica-slate of the Urals. It was named after Czar Alexander II because it shows the Russian colours of green and red.
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In geology, the term Algonkian describes a period or era recognized by the United States Geological Survey and some other authorities, between the Achaean and the Palaeozoic, from both of which it is generally separated in the record by unconformities. Algonkian rocks are both sedimentary and igneous. Although fossils are rare, life certainly existed in this period.
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Alkaline rock refers to any rock which contains more than average amounts of potassium bearing and sodium bearing minerals.
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Allanite is a silicate containing a large amount of cerium. It is usually black in colour, opaque, and is related to epidote in form and composition. It occurs as a minor constituent of many igneous rocks and is frequently associated with epidote. Found in some magnetic bodies. It has the formulae (Ce,Ca,Y)2(Al,Fe)3(SiO4) 3(OH) and a relative hardness of 6. It is named after T. Allan who discovered it.
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Allemontite is a natural alloy of arsenic and antimony. It has a relative hardness of 4.
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In minerals, an allomorph is any one of two or more distinct crystalline forms of the same substance; or the substance having such forms, for example carbonate of lime occurs in the allomorphs calcite and aragonite. The term
allomorph describes a variety of pseudomorph which has undergone a partial or complete change or substitution of material. Thus limonite is frequently an allomorph after pyrite.
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Allophane is a mixture of minerals bound together in a gel and found in cavities and fissures in metal-bearing ore veins and in some coal deposits. Often
allophane is comprised of about 35 percent aluminium oxide, between 22 and 28 percent of another silica compound. Because of its variable composition and shape, allophane occurs in many different shapes and colours.
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Alluvium are deposits of earth, sand, gravel, and other transported matter, made by rivers, floods, or other causes, upon land not permanently submerged beneath the waters of lakes or seas. They are often found covering a pediment.
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Almandine is a variety of precious garnet, reddish or violet in colour. It is named after Alabanda, a town in Caria, where it was first and is chiefly found.
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Alteration refers to physical or chemical change in a rock or mineral after its original formation. Can result in new minerals or in textural changes in the rock.
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Alum schist or alum slate is a variety of shale or clay slate, containing iron pyrites, the decomposition of which leads to the formation of alum, which often effloresces on the rock. It is named on account of much alum being prepared from it. It is greyish, bluish, or iron-black in colour; often possessed of a glossy or shining lustre; chiefly composed of clay (silicate of alumina), with variable proportions of sulphide of iron (iron pyrites), lime, bitumen, and magnesia.
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Alum stone is a mineral of a grayish or yellowish-white colour, approaching to earthy in its composition, from which (in Italy) is obtained a very pure alum by simply subjecting it to roasting and lixiviation.
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Alumina (Al2O3) is the single oxide of the metal aluminium. As found native it is called corundum, when crystallized ruby or sapphire, when amorphous emery. It is next to the diamond in hardness. In combination with silica it is one of the most widely distributed of substances, as it enters in large quantity into the composition of granite, traps, slates, schists, clays, loams, and other rocks. The porcelain clays and kaolins contain about half their weight of this earth, to which they owe their most valuable properties. It forms compounds with certain colouring matters, which causes it to be employed in the preparation of the colours called lakes in dyeing and calico-printing. It combines with the acids and forms numerous salts, the most important of which are the sulphate (Alum) and acetate, the latter of extensive use as a mordant.
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Alunite (alum stone) is a hydrated aluminium and potassium sulphate secondary mineral usually formed by sulphuric acid solutions acting on rocks rich in alkalic feldspar. It is used in the production of alum, the manufacture of styptic pencils, as a dye fixer in the treatment of leather and as a white pigment in paint. It has the formulae KAl3(SO4)2(OH)6 and a relative hardness of 4. Alunite was mined since the 15th century, but was only identified as a distinct mineral in 1824.
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Alunogen is a fibrous aluminium sulphate found in volcanic debris, clays, felspathic rocks which contain pyrites, and often as an inflorescence on the walls of mines and caves.
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Amalgams are alloys of mercury and other metals. Mercury has the ability to dissolve many metals and to form new liquid or solid alloys. This is why mercury has always been used and always will be used in mining for precious metals such as gold and silver. The rocky gravel containing ores of gold and silver intermingles with mercury; amalgams develop and through the vaporization of mercury, pure metal results. It is most widely known that silver amalgams also occur as a natural mineral. They appear in the form of tiny marbles or grains or flakes. They always accompany drops of mercury, for they develop jointly through the weathering of cinnabar. The main deposits of silver amalgams are in Bavaria and Chile. In Colombia a natural gold amalgam has been found. All metals except iron and platinum form
amalgams. Amalgams are used extensively in dentistry for filling teeth,
amalgams were found in 1998 to damage the immune system and are likely to be one of the causes of AIDs.
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Amber is a yellowish or reddish-brown, brittle, translucent resin resembling copal, found as a fossil in alluvial soils, with beds of lignite, or on the seashore in many places. It is easy to cut with a knife, burns with a yellow flame emitting a pungent smoke and takes a fine polish, and is used for pipe mouthpieces, beads, etc., and as a basis for a fine varnish. By friction, it becomes strongly electric.
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Amblygonite is a rare mineral occurring in lithium and phosphate rich granite pegmatites. Associated with spodumene, apatite, tourmaline, lepidolite. It has the formulae (Li,Na)Al(PO4)(F,OH) and a relative hardness of 6.
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Amethyst is a purple or bluish-violet coloured precious stone comprised of quartz coloured with manganese. It is so named from the ancient Greek's belief that it had the power to cure drunkenness.
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Amianthus is a soft, silky variety of asbestos.
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Amorphous refers to 'Without form'. The term is applied to rocks and minerals that lack definite crystal structure.
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Ampelite is an earth abounding in pyrites, it was formerly used by the ancients to kill insects, etc. , on vines. The term was applied by Brongniart to a carbonaceous alum schist.
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The amphiboles are a large group of minerals, the silicates of many different bases, the commonest being alumina, iron oxide, lime, magnesia and the alkalis. They are constituents of many crystalline igneous rocks and of metamorphic schists. In many of their properties they closely resemble the pyroxenes. They occur generally in black or dark green crystals, usually long, narrow and blade-like, and owing to their perfect cleavages their surfaces are smooth and bright. The commoner varieties are hornblende, actinolite and tremolite.
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Amygdaloidal is a name given to igneous rocks, usually old lava flows, full of almond-shaped cavities which have been filled up with secondary minerals, such as calcite, agate or the zeolites. These cavities vary in size up to several centimetres across and were formed while the rock was still fluid and in motion.
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Amygdule refers to a mineral-containing cavity in an igneous rock formed by escaping gas. An unfilled cavity is known as a scoria.
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Analcime is a mineral of the zeolite group noted for its vitreous lustre, and has the formulae NaAlSi2O6ù2H2O and a relative hardness of 6. It is found in the cavities of intrusive and volcanic igneous rocks; often as clear shiny crystals and is associated with calcite and other zeolites. Analcime was first identified on islands off Sicily and was confirmed as a distinct mineral in 1797 by the French mineralogist Rene-Just Hauy.
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Anatase is one of the crystalline forms of titanium oxide, and an important source of the metal titanium. Anatase has the formulae TiO2 and a relative hardness of 6. It is found in granite, gneiss, mica schist, metamorphic limestone, and dolomite. Anatase may be present as an accessory mineral in the rocks or in a quartz vein traversing it. It is used as a coating for welding rods and as a source of titanium.
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Anchor Ice is a rare phenomena occurring in rivers where the current is too strong for the formation of ice on the surface, but where ice forms on the bottom. This ice may encircle a stone or other object (such as a ship' s anchor, hence the name), causing it to float to the surface when sufficient ice has formed.
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Andalusite is a mineral formed by the metamorphism of aluminous shales and slate. It is used in the manufacture of spark plugs and other porcelains and may serve as a gem stone if it is clear and transparent, and exhibits the optical phenomenon of pleochroism - that is the capacity to appear in different colours when viewed in different lights and from different angles. It is named from Andalusia, a province of Spain where it was first discovered. It has the formulae Al2SiO5 and a relative hardness of 8.
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Andesine is a kind of triclinic feldspar found in the Andes. It has the formulae NaAlSi3O8 and a relative hardness of 6.
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Andesite is a crystalline igneous rock, occurring mostly in lava flows, but sometimes in dykes and veins. It consists principally of plagioclase feldspar, and is often porphyritic, showing large crystals of feldspar scattered through a fine-grained mass, usually of small feldspar crystals, but often containing much glassy material. Andesite forms most of the recent volcanic rock of the Andes, and is thus named after the Andes.
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Anglesite is a common, minor ore of lead formed by the oxidation of galena. It has the formulae PbSO4 and a relative hardness of 3. It is found in the upper, oxidized portions of lead veins and is named after the Island of Anglesey.
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Anhydrite is a mineral consisting of sulphate of lime. It has rectangular cleavage fragments and occurs in a manner similar to gypsum and often found with it but not as common. It is found in the cap rock of salt domes and in limestone rocks. The name comes from the Greek meaning 'without water' . It has the formulae CaSO4 and a relative hardness of 4.
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Ankerite is a mineral closely related to dolomite, but containing iron. Ankerite was first identified in Styria, Austria and was confirmed as a distinct species in 1825. It is named after mineralogist Professor Mathias Anker of Austria.
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Annabergite (also known as nickel bloom) is a rare secondary mineral of a pale green colour, that forms in the oxidation zones of ore deposits and is found as a powdery coating on the surface of nickel-bearing minerals such as chloanite and nickeline. Annabergite is a hydrated arsenate of nickel of the vivanite group.
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Annivite is a variety of terahedrite containing bismuth and usually iron and zinc.
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Anorthite is a widely distributed and abundant rock-forming feldspar. It has the formulae (Na,Ca) AlSi3O8 and a relative hardness of 7.
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Anorthoclase is a feldspar closely related to orthoclase, but triclinic. It is chiefly a silicate of sodium, potassium, and aluminium.
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Anthophyllite is a mineral occurring in crystalline schists rich in magnesium. It has the formulae (Mg,Fe) 7Si8O22(OH)2 and a relative hardness of 6.
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Anthracite (glance, blind-coal, stone coal or parrot-coal) is a kind of non-bituminous coal of a shining lustre, approaching to metallic, distinguished by its great hardness, its high proportion of carbon, and the great heat given out in burning without smoke, with a weak or no flame. It is sometimes called parrot-coal on account of the crackling or chattering noise it makes when burnt.
Anthracite is found in England, Scotland, and Ireland, and in large quantities in the United States, chiefly in Pennsylvania.
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Anthraconite (stinkstone or swinestone) is a coal-black marble, usually emitting a fetid smell when rubbed, hence its alternative names.
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An anticlinal line or anticlinal axis is a line from which strata dip in opposite directions, like the ridge of a roof.
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An anticlinorium is an upward elevation of the earth's crust, resulting from a geanticlinal.
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Antigorite is an iron-bearing secondary mineral found in serpentine. Antigorite is a hydrous silicate of magnesium and iron and belongs to the kaolinte-serpentine group of minerals. It has a green or yellowish-green colour and has a resilient structure making it suitable for carving and polishing, often being sold as a cheap artificial jade.
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Antimonite is an antimony ore. It was used by the Greeks as a cosmetic for darkening the eyelids.
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Antimony or stibium is a brittle, silver-white, pentavalent semimetal element with the symbol Sb and a relative hardness of 3 or 4. Antimony, also known as grey antimony, is easily pulverised into a powder and was long used as a cosmetic for blackening around the eyes, the Greeks and Romans using antimony to darken their eye lids and eye lashes and Arab peoples still use it as such. Black antimony or stibnite (also known as antimonite and antimony glance) is actually antimony trisulphide, and is the most common ore of antimony occurring as grey striated prismatic crystals of the orthorhombic system.
Antimony is found in many places, including France, Spain, Hungary, Italy, Canada, Australia, and Borneo. The metal, or, as it was formerly called, the regulus of antimony, does not rust or tarnish when exposed to the air. When alloyed with other metals it hardens them, and is therefore used in the manufacture of alloys, such as Britannia-metal, type-metal, and pewter. In bells it renders the sound more clear; it renders tin more white and sonorous as well as harder, and gives to printing types more firmness and smoothness. The salts of antimony are very poisonous. The protoxide is the active base of tartar emetic and James's powder, and is justly regarded as a most valuable remedy in many diseases.
Yellow antimony is a preparation of antimony of a deep yellow colour, used in enamel and porcelain painting. It is of various tints, and the brilliancy of the brighter hues is not affected by foul air.
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Apatite is a widely distributed accessory constituent in all classes of rock. Found in crystals and masses, crystallised apatite has been extensively used for fertiliser. Transparent varieties of a fine colour are sometimes used for gems - but it's too soft for extensive use. Apatite has the formulae Ca5(F,Cl,OH)(PO4)3 and a relative hardness of and crystallizes in a regular six-sided prism, usually terminated by a truncated six-sided pyramid. It passes through various shades of colour, from white to yellow, green, blue, and occasionally red, scratches fluorspar but is scratched by felspar, and has a specific gravity of about 3.5. It is a compound of phosphate of lime with fluoride and chloride of calcium.
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Aphanite is a very compact, dark-coloured rock, consisting of hornblende, or pyroxene, and feldspar, but neither of them in perceptible grains.
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Aphanitic rock refers to a rock in which the crystalline constituents are too small to be distinguished without magnification.
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Apophyllite (so called from its foliated structure or easy cleavage), also called fish-eye stone is a hydrothermal mineral filling cavities in basalt and tufaceous rocks. It is associated with stilbite, scolecite, calcite, prehnite, analcime. It has the formulae KCa4Si8O2O(OH)ù8H2O and a relative hardness of 5.
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Aquamarine is a variety of beryl forming delicate bluish-green coloured hexagonal prisms in granite pegmatites and drusy cavities. It is used as a gem stone. It has the formulae Be3Al2Si6O18 and a relative hardness of 7.
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Aqueous rock is another name for sedimentary rock.
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Aragonite (named from Aragon in Spain) is a mineral identical in composition with calcite or carbonate of lime, but differing from it in its crystalline form and some of its physical characters. It forms easily in a sedimentary environment but only stable in metamorphic rocks formed at high temperatures. It has the formulae CaCO3 and a relative hardness of 4.
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The Archaean is the earliest period in geological period, extending up to the Lower Silurian. It includes an Azoic age, previous to the appearance of life, and an Eozoic age, including the earliest forms of life. This is equivalent to the formerly accepted term Azoic, and to the Eozoic of Dawson.
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The archeozoic period was the first geological period. It was characterised by an absence of animal life and extensive volcanic activity.
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Arenite is a sandy sedimentary rock composed of eroded fragments of pre-existing rocks. The individual particles are of about the same size as sand grains, thus they include grits and siltstones as well as sandstones. Rocks of this type can be of marine, fresh-water, terrestrial, or glacial origin. Quartz sandstone is the most common type, and the terms 'arenite' and 'sandstone' are often used interchangeably. Special types of arenaceous rocks include greywackes, greensands, and arkose.
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Arfvedsonite is a black or greenish black mineral of the amphibole group.
Arfvedsonite is typical of alkaline plutonic rocks that are rich in iron. It has the formulae Na2- 3(Fe,Mg,Al) 5Si8O22(OH,F)2 and a relative hardness of 6.
Arfvedsonite was first discovered in Greenland, and was named after the Swedish chemist Johan Arfvedson.
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Argentine is a siliceous variety of calcite, or carbonate of lime containing a little silica, having a silvery-white, pearly lustre, and a waving or curved lamellar structure. It is found in primitive rocks and frequently in metallic veins.
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Argentite is an important primary silver ore. The name is from Latin meaning 'silver'. Occurs disseminated in galena and in the cementation zone of lead and zinc deposits. Associated with cerussite, chlorargyrite, native silver. It has the formulae Ag2S and a relative hardness of 3.
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Argillaceous rocks (or argillites) are clayey sedimentary rocks of fine-grained sediments composed of particles that are less than 0.0625 mm in size. Mudstones, clays, shales, marls, and silts are all examples. Most argillaceous rocks contain material of two types: clay minerals and rock flour, the latter consisting of very fine particles of quartz, feldspar, and other rock-forming minerals. The great majority of argillaceous rocks have been deposited in water, whether in the sea, in estuaries, or in lakes. There are also terrestrial deposits in this category, such as loess and clays of glacial origin.
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Argillite is a usually bluish or dark grey coloured, but sometimes greenish grey or brownish-red coloured argillaceous schist or slate (clay slate).
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Arkose is a dark red or brownish coloured sedimentary rock resembling granite, formed from feldspar-rich sediment deposited on land or in water. Arkose is a form of sandstone abundant in many parts of the world, and chiefly composed of granite and gneiss sediments.
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Arsenate refers to minerals in which a compound of arsenic and oxygen (AsO4) is an important part.
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Arsenic is a trivalent and pentavalent, solid, poisonous common element usually found combined with metals as arsenides, the commonest of which is arsenical pyrites, FeAsS. It has a steel colour and high metallic lustre, and tarnishes on exposure to the air, first changing to yellow, and finally to black. In hardness it equals copper; it is extremely brittle, and very volatile, beginning to sublime before it melts. It burns with a blue flame, and emits a smell of garlic. Its specific gravity is 5.76. It forms compounds with most of the metals. Combined with sulphur it forms or-piment and realgar, which are the yellow and red sulphides of arsenic. Orpiment is the true arsenicum of the ancients. With oxygen arsenic forms two compounds, the more important of which is arsenious oxides or arsenic trioxide (As40e), which is the white arsenic, or simply arsenic of the shops. It is usually seen in white, glassy, translucent masses, and is obtained by sublimation from several ores containing arsenic in combination with metals, particularly from arsenical pyrites.
Of all substances arsenic is that which has most frequently occasioned death by poisoning, both by accident and design. The best remedies against the effects of arsenic on the stomach are ferric hydroxide or magnesic hydroxide, or a mixture of both, with copious draughts of bland liquids of a mucilaginous consistence, which serve to procure its complete ejection from the stomach. Oils and fats generally, milk, albumen, wheat-flour, oatmeal, sugar or syrup, have all proved useful in counteracting its effect. Like many other virulent poisons it is a safe and useful medicine, especially in skin diseases, when judiciously employed. It is used as a flux for glass, and also for forming pigments. The arsenite of copper (Scheele's green) and a double arsenite and acetate of copper (emerald green) were formerly largely used to colour paper-hangings for rooms, but as poisonous gases are liable to be given off, the practice was abandoned. Arsenic compounds have in the past been used for colouring confectionery, and other articles, bright green. It is found in crude oil of vitriol, and occasionally in the past in products such as grape-sugar, beer, etc, in the manufacture of which oil of vitriol was employed. Arsenic tablets were formerly worn as protection against the plague.
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Arsenopyrite (mispickel) is the most common mineral containing arsenic. It occurs as a tin-white coloured, metallic lustred mineral with tin and tungsten ores in high temperature deposits as a deposition from hot waters. Frequently associated with gold. Also found with copper and silver ores. It has the formulae FeAsS and a relative hardness of 6.
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Artinite is both a hydrous and a hydrated white mineral occurring in serpentine and other igneous rocks. Artinite has monoclinic crystals, and is found both as massive aggregates and in sprays of needle-shaped growths. Artinite was confirmed as a distinct species in 1903 and named after the mineralogist Ettore Artinini.
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Asbestos is a fibrous mineral with a high melting and combustion point. It is a variety of amphibole or of pyroxene, occurring in long and delicate fibres, or in fibrous masses or seams, usually of a white, grey, or green-grey colour. The name is also given to a similar variety of serpentine. The finer varieties have been wrought into gloves and cloth which are incombustible. The cloth was formerly used as a shroud for dead bodies, and has been recommended for firemen's clothes. Asbestos in also employed in the manufacture of iron safes, and formerly for fireproof roofing, and for lamp wicks. Some varieties are called amianthus. Asbestos is now known to be a highly dangerous mineral, causing severe and often fatal respiratory problems when the dust is breathed.
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Ashphaltum is a dark brown or black form of bitumen, the purest varieties are used in the manufacture of black Japan, other varieties in the production of bituminous paints.
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Asphalt or Asphaltum is the most common variety of bitumen. It is also called mineral pitch. Asphalt is a compact, glossy, brittle, black or brown mineral, which breaks with a polished fracture, melts easily with a strong pitchy odour when heated, and when pure burns without leaving any ashes. It is found in the earth in many parts of Asia, Europe, and America, and in a soft or liquid state on the surface of the Dead Sea, which from this circumstance was called Asphaltites. It is of organic origin, the asphalt of the great Pitch Lake of Trinidad being derived from bituminous shales, containing vegetable remains in the process of transformation. Asphalt is produced artificially in making coal-gas. During the process much tarry matter is evolved and collected in retorts. If this be distilled, naphtha and other volatile matters escape, and asphalt is left behind. It is sometimes called Jew's Pitch.
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Asphalte Rock or asphalt rock, is a limestone impregnated with bitumen, found in large quantities in various localities in Europe, as in the Yal de Travers, Neufchatel, Switzerland; in the department of Ain in France; in Alsace, Hanover, Holstein, Sicily, etc. These rocks contain a variable quantity of bitumen (from 7 or 8 to 20 or 30 per cent) naturally diffused through them. The Yal de Travers asphalt was discovered in 1710. In 1837 an English patent was taken out for its application to roads, pavements, terraces, areas, roofs, etc. Since then other asphalte-rocks, as well as artificial preparations made by mixing bitumen, gas-tar, pitch, or other materials, with sand, chalk, etc, have been brought into competition with it.
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Asteria is the name applied to a variety of corundum, which displays an opalescent star of six rays of light when cut with certain precautions. The name is also applied to the cat's-eye, which consists of quartz, and is found especially in Sri Lanka.
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Asterism is n optical effect in which a four- or six-rayed star can be seen in a mineral.
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Astrophyllite is a complex mineral with a monoclinic crystalline structure, containing up to five different metals, and formed in cavities and fissures in syenite and other igneous rocks. The crystals of astrophyllite are often shiny and appear in thin sheets with pointed ends resembling foliage. Chemically,
astrophyllite is a hydrous silicate of potassium, sodium and titanium, but may also feature iron, or manganese or both. Astrophyllite was confirmed as distinct species in 1854.
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Atacamite is the native hydrous oxychloride of copper. It is a comparatively rare mineral occurring in arid regions in the upper oxidised zone of copper deposits. It has the formulae Cu2Cl(OH)3 and a relative hardness of 4. It is named after the desert of Atacama in South America, where it is found.
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Augite is an important rock forming mineral of the pyroxene group. Chiefly found in dark coloured igneous rocks, especially those whose magmas were rich in iron, calcium and magnesium. Seldom found in rocks that contain much quartz. A common member of the pyroxene group. Told from the amphibole group by cleavage. It has the formulae (Ca,Na) (Mg,Fe,Al,Ti)(Si,Al)2O6 and a relative hardness of 6. When crystallized it assumes the form of short, slightly rhombic prisms, with their lateral edges replaced, and terminated at one or both extremities by numerous planes. A transparent green variety found at Zillerthal, in the Tyrol, is used in jewelry.
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Aurichalcite is a hydrous carbonate of copper and zinc, found in pale green or blue crystalline aggregations. It yields a kind of brass on reduction.
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In geology the term autoclastic describes rocks having a broken or brecciated structure due to crushing, in contrast to those of brecciated materials brought from a distance.
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Autunite is a secondary mineral found in the zone of oxidation and weathering of uranite or other uranium minerals. It has strong fluorescence and is used as an ore of uranium. It has the formulae Ca(UO2)2(PO4)2ù10- 12H2O and a relative hardness of 3.
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Aventurine is a variety of translucent quartz, spangled throughout with scales of yellow mica.
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Axinite is a mineral, a silicate of alumina, lime, etc, with boracic acid, deriving its name from the form of the crystals, the edges of which bear some resemblance to the edge of an axe. Axinite occurs in cavities in granite and in the contact zones surrounding granite intrusions. It has the formulae Ca2(Fe,Mn)Al2(BO3)(Si4O12)(OH) and a relative hardness of 7.
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Axstone (axe-stone) is a variety of jade. It is used by some native peoples, particularly the natives of the South Sea Islands, for making axes or hatchets.
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Azoic (without life) is a name given to rocks devoid of fossils.
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The Azoic age was the age preceding the existence of animal life, or anterior to the Palaeozoic tome.
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Azurite is a minor ore of copper with an intense azure-blue colour. It alters to malachite and is associated with limonite, calcite, chalcocite, chrysocolla and other secondary copper minerals.
Azurite reacts vigorously with hydrochloric acid. It has the formulae Cu3(CO3) 2(OH)2 and a relative hardness of 4.
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Abbreviations
Rocks & Minerals
