Gabbronite or gabronite is, a mineral, a variety of scapolite, occurring' in masses, whose structure is more or less foliated, or sometimes compact. Its colours are grey, bluish or greenish grey, and sometimes red. Research Gabbronite
Gabbros are basic rocks solidified under great pressure at considerable depths in the earth's crust. They are coarse-grained and consist of plagioclasefeldspar with augite. Sometimes the term is used to include similar rocks composed of the same feldspar with other minerals, and according to the minerals contained they are known as norites, troctolites, eucrites, etc. Research Gabbros
Gadolinite, named after the Russian chemist Gadolin, or ytterbite is a naturally occurring complex silicate containing beryllium, iron and many of the rare earth metals, of which the latter is an important source. The principal rare earths that occur in gadolinite are yttrium and erbium, together with smaller amounts of cerium and lanthanum.It is usually found in dull, amorphous masses disseminated through granite; is black, or very dark green in colour, with a resinouslustre. *Gahnite
Gahnite (zinc spinel) is a dark green mineral of the spinel group consisting of zincaluminiumoxide. It is named after J G Gahn the Swedish chemist. Research Gadolinite
Galena (lead sulphide) or galenite is virtually the only source of lead and an important ore of silver. It is found both in masses and crystallized in cubes, but sometimes in truncated octahedra and has the formulae PbS and a relative hardness of 3. It is a very common metallic mineral, its colour is bluish-grey, like lead, but brighter; its lustre metallic; texture foliated; fragments cubical; soft, but brittle. When found in veins that show a connection to igneous rocks, it is frequently found with silver minerals. Galena is also found in limestones either as veins or as a replacement deposit.
Galena effervesces with nitric and hydrochloric acids. For the most part it contains about 86.6 per cent of lead and 13.4 of sulphur, generally some silver, and also antimony, zinc, iron, and bismuth. Where the proportion of silver is high it is known as argentiferous galena, and worked with a view to the extraction of this metal. Galena occurs principally in the older or primary rocks, being found in England mainly in the Mountain Limestone (base of the Carboniferousformation). In the United States it is very abundant, the deposit of galena in which the mines of Illinois are situated being extensive and important. Research Galena
Gannister is a very siliceous close-grained variety of clay with a poor alkali content found especially under coal seams in the Coal Measures of northern England. Research Gannister
Garnet is a widely distributed group with several minerals. They are found in both metamorphic and igneous rocks. The chief use of red transparent garnets are as an inexpensive gem stone, however, much is used as an abrasive material. They have the formulae A3B2(SiO4)3 and a relative hardness of 8. The commonest colour of garnet is red and the lustre is vitreous. The dodecahedron and trapezohedron are the common forms. There are also white, green, yellow, brown, and black varieties. The garnet is a silicate, the bases being aluminalime (grossularite, essonite, or cinnamon stone), or alumina magnesia (pyrope), or alumina iron (almandine), or aluminamanganese (spessarite), or iron lime (common garnet, melanite, allochroite), or chromiumlime (ouvarovite, the colour emerald green). The garnet was, in part, the carbuncle of the ancients. Garnet is a very common mineral in gneiss and micaslate. Research Garnet
Garnierite is an ore of nickel. It's probably formed as an alteration of nickel bearing peridotites. It has a nice apple green colour and the formulae (Ni,Mg)6Si4O10(OH)8. It has a relative hardness of 4. It is named after the French geologist Jules Garnier. Research Garnierite
The Gault is a series of beds of clay and marl in the South of England, between the upper and lower greensand of the Cretaceous period. They vary in colour from a light grey to a dark blue, and are developed chiefly in the neighbourhood of Folkestone (hence oftenc called Folkestone marl). Research Gault
Geanticlinal is an upward bend or flexure of a considerable portion of the earth's crust, resulting in the formation of a class of mountain elevations called anticlinoria. Research Geanticlinal
Gems, or precious stones, are sometimes found crystallized in regular shapes and with a natural polish, more commonly they are of irregular shapes and with a rough coat.
The term gem often denotes more particularly a stone that is cut, polished, or engraved, and it also includes pearls and various artificial productions.
The first and most valuable class of gems includes diamonds, emeralds, rubies, sapphires, and a few others; the second class includes the amethyst, topaz, garnet, etc;
while agate, lapis-lazuli, cornelian, etc, though much used for ornament, can scarcely be called gems.
The fabrication of artificial gems became an important industrial art during the 19th century. The base of one class of imitations is a peculiar kind of glass of considerable hardness, brilliancy and refractive power called paste or strass, which is distinguished from ordinary glass by the presence of 50 per cent of oxide of lead among its constituents. When the strass is obtained very pure it is melted and mixed with substances having a metallic base, generally oxides, which communicate to the mass the most varied colours.
Another class, called semi-stones or doublets, are made by affixing thin slices of real gem to an under part of strass by means of an invisiblecement. In some cases an imitation is made by setting uncoloured strass or quartz in jewelry with some coloured 'foil' at the back of it.
At the end of the 19th century attempts were made with a fair measure of success to manufacture true gems by artificial processes. The French chemists Becquerel, Ebelman, Gaudin, Despretz, and others did much in this direction.
In 1858 Deville and Caron communicated to the Academy of Sciences, Paris, a process for the production of a number of gems of the corundum class, such as rubies, sapphires, etc. The process essentially consisted in exposing the fluoride of aluminium, together with a little charcoal and boracic acid, in a plumbagocrucible protected from the action of the air, to a white heat for about an hour. Many experiments with a view to producing diamonds artificially have also been made. From hydrocarbons, subjected to a very intense heat and enormous pressure, minute crystals, differing from natural diamonds in no respect save brilliancy, have been produced. Artificial diamonds are now widely used in industry.
In art and archaeology the term gem is usually applied to a precious stone cut or engraved in ornamental designs, or with inscriptions. Stones on which the design is raised above the general surface are called cameos; those having the design sunk below the surface are called intaglios. Early specimens of cut gems are seen in the scarabaei or beetle-shaped signets worn in rings by the ancient Egyptians. Among the Greeks, Etruscans, and Romans gem-sculpture held a high place, reaching its highest point under Augustus. Modern gem-engraving dates from the beginning of the 15th century, the chief seats of the art being Italy and Germany. Rome becoming the headquarters of the seal-engraving art. The traditional tools of the engraver consist of a lathe, and a series of little rods with heads of different shapes, all of which can be adjusted to the lathe. The axis of the lathe is pierced at the centre with an orifice, into which the tools for cutting the stone are firmly fixed by means of a screw. The engraver wets the extremity of the mounted rod with diamond dust made into a paste with oil (traditionally olive oil), and as the wheel is in motion he applies the stone, firmly cemented to a piece of reed, to the revolving tool. The diamond dust enables the tool to cut into the stone with ease. As the design is frequently very elaborate and of the greatest delicacy, the tools are necessarily multiform. The stones used for cameo-cutting often exhibit layers of different colours, so that the raised design has a tint distinct from the ground. Intaglios are very often executed in transparent stones, and the subjects treated in this manner are more limited in number. They are chiefly such as seals, devices, coats of arms, etc. Research Gems
Geochronology is the branch of geology concerned with ordering and dating of events in the earth's history, including the origin of the earth itself. Research Geochronology
A geode is a round hollow nodule containing earthy matters, sometimes quartz, sometimes agate.
Geodes are found in most volcanic rocks and are formed by water depositing materials in the hollows of these rocks. Research Geode
Geodynamics is the branch of geology concerned with the forces and processes, especially on a large- scale, of the earth's interior, particularly as regards their effects on the crust or lithosphere. Research Geodynamics
geomorphology or geomorphogeny is the branch of geology that is concerned with the structure, origin, and development of the topographical features of the earth's crust. Research Geomorphology
Geosynclinal is the downward bend or subsidence of the earth's crust, which allows of the gradual accumulation of sediment, and hence forms the first step in the making of a mountain range. Research Geosynclinal
Geyserite is a loose hydrated form of silica, a variety of opal, deposited in concretionary cauliflower-like masses, around some hot springs and geysers. Research Geyserite
Gibbsite is a primarily secondary mineral named after George Gibbs, an American mineralogist. Gibbsite is a hydrate of alumina and gives off a clay-like smell when rubbed or breathed on. It is an important ore of aluminium. Typically it occurs massive, but rarely crystals are found in flattened, tubular, pseudo-hexagonal shapes. It is mostly white, reddish white or colourless with shades of grey, blue and green and a pearly or vitreouslustre. Research Gibbsite
Girasole (girasol) is a variety of opal which is usually milk white, bluish white, or sky blue in colour but in a bright light reflects a reddish colour. The brightest are found in Brazil and Siberia. The name is sometimes bestowed on the Asteriasapphire. One variety is known as the fire opal. Research Girasole
The glacial epoch was a period during which the climate of the modern temperate regions was polar, and ice covered large portions of the northern hemisphere to the mountain tops. Research Glacial Epoch
Glacier tables are large stones found on glaciers supported on pedestals of ice. The stones attain this peculiar position by the melting away of the ice around them, and the depression of its general surface by the action of the sun and rain. The block, like an umbrella, protects the ice below it from both; and accordingly its elevation measures the level of the glacier at a former period. By and by the stone table becomes too heavy for the column of ice on which it rests, or its equilibrium becomes unstable, whereupon it topples over, and falling on the surface of the glacier defends a new space of ice, and begins to mount afresh. Research Glacier Tables
Glacier theory is the theory that large parts of the frigid and temperate zones were covered with ice during the glacial, or ice, period, and that, by the agency of this ice, the loose materials on the earth's surface, called drift or diluvium, were transported and accumulated. Research Glacier Theory
Glance is a name given to some sulphides, mostly dark-coloured, which have a brilliant metallic lustre, such as the sulphide of copper which is called copper glance. Research Glance
Glauberite, named after the 17th century German chemist Glauber, is a bitter salty tasting mineral that dissolves slowly in water. It is a sedimentary mineral formed by the evaporation of saline water. It slowly alters to gypsum when exposed to air. It has the formulae Na2Ca(SO4)2. Research Glauberite
Glauconite is a mineral of marine origin and found in sedimentary deposits of various kinds. It is the green mineral characteristic of the greensand of the chalk and other formations. It is similar to a mineral called celadonite, it is used in the textile, sugar, and brewing industries; as a colouring agent and in the manufacture of fertilizers. It has the formulae (K,Na)(Al, Fe,Mg)2(Al,Si) 4O10(OH)2 and a relative hardness of 2. Research Glauconite
Glaucophane is a dark-blue sodium rich rock forming mineral which, like other amphiboles, is poor in silica. It is of interest to petrologists in helping to define the metamorphic conditions which formed the surrounding rock. It has the formulae Na2(Mg,Fe)3Al2Si8O22(OH)2 and a relative hardness of 7. It often has a blue colour. Research Glaucophane
Gneiss refers to a crystalline rock, consisting, like granite, of quartz, feldspar, and mica, but having these materials, especially the mica, arranged in planes, so that it breaks rather easily into coarse slabs or flags. Hornblende sometimes takes the place of the mica, and it is then called hornblendic or syenitic gneiss. Similar varieties of related rocks are also called gneiss. Research Gneiss
Goethite is an ore of iron and a common mineral. Usually formed as a weathering product of iron bearing minerals. The term 'limonite' is commonly used for earthy yellow and brown goethite. It has the formulae FeO (OH) and a relative hardness of 6. Research Goethite
Gold is a bright yellow coloured, rare, precious metal element with the formulae Au and a relative hardness of 3 occurring in nature in widely distributed small amounts. The main source of gold is in gold-quartz veins where gold was deposited from mineral bearing solutions. When the veins weather, the gold is separated from the quartz and mechanically settles on the stream floor as a placer deposit. The fineness of gold is measured in carats. 24 carat gold is pure, 22 carat gold is 22 parts gold to two parts other metals and so on. Gold is seldom used for any purpose in a state of perfect purity on account of its softness, but is combined with some other metal to render it harder. Standard gold, or the alloy formerly used for the gold coinage of Britain, consists of twenty-two parts of gold and two of copper (being thus 22 carats fine). Articles of jewelry are made of every degree of fineness up to 22 carats, i.e. 22 parts of gold to 2 of alloy.
Gold is one of the most ductile and malleable of all the metals It is one of the heaviest of the metals, and not being liable to be injured by exposure to the air, is well suited for making coins and jewelry. Its ductility and malleability are very remarkable. It may be beaten into leaves so exceedingly thin that one grain in weight will cover 56 square inches. It is also extremely ductile; a single grain may be drawn into a wire 500 feet long, and an ounce of gold covering a silver wire is capable of being extended upwards of 1300 miles. It may also be melted and remelted with scarcely any diminution of its quantity. It is soluble in nitro-muriatic acid or aqua regia, and in a solution of chlorine. Its specific gravity is 19.3, or it is about nineteen times heavier than water.
The alloy of gold and silver is found already formed in nature. It is of a paler yellow than pure gold, while the copperalloy has a colour bordering upon reddish yellow. Palladium, rhodium, and tellurium are also met with as alloys of gold.
Gold has been found in larger or smaller quantities in nearly all parts of the world. It is commonly found in reefs or veins among quartz, and in alluvial deposits. Among the latter may be ranked the deposits in river beds, from which the gold is obtained by dredging. Dredging is even employed where the water has to be brought by artificial means. When gold is in rock, quarrying, crushing, washing, and treatment with mercury are employed. The rock is crushed by machinery, and the crushed material is treated with mercury, which dissolves the gold, forming a liquid amalgam, after which the mercury is volatilized, and the gold left behind. Two other processes are also in use, viz. the chlorination and the cyanide. In the former the gold is transformed into soluble gold chloride, and the metal is obtained from this solution by means of sulphuretted hydrogen. The cyanide process is especially useful for ores containing tellurium, or for ores in a fine state of division, and con^sists in dissolving the metal in potassiumcyanide solutions, from which it can be obtained by various means. The gold obtained by these methods always contains silver, from which it is separated by the process known as 'parting'.
In alluvial (or placer) deposits it is extracted by washing, in the form of dust, grains, laminae, or nuggets. After the gravel has been turned over and the nuggets have been taken out, the remainder is washed to recover the finer particles of gold. In washing in the pan - 'panning out' - a quantity of the 'dirt', free from stones, is put into a shallow dish with a slight depression in the middle. It is then mixed with water, and the dish held with one side lower than the other, while by a gentle motion the sand and other lighter bodies are washed over the edge of the pan, and the heavy matters containing the gold remain at the bottom. The 'dolly' or 'tossing tub' is a circular tub for washing rather fine stuff that has been sifted. The 'cradle' consists of a short box or trough two meters long, mounted on a kind of rockers, and slightly inclined to allow the mud to run off. A box, with a bottom of iron plate perforated with holes, is placed over the higher end of the trough. The 'pay dirt' (i.e. gravel or sand containing a sufficient amount of gold to be profitably worked) is thrown into this box, and water is run or poured upon it. The finer portion is thus carried through the holes, and directed by an inclined plate into the trough. The cradle is rocked from side to side, the light matters are carried away by the water, and the particles of gold and other heavy matters lodge behind the 'rimes', or transverse bars of wood, with which the bottom of the trough is fitted, and are afterwards collected.
Where practicable, the method known as 'sluicing' is often adopted for treating alluvial deposits. The 'sluices' consist of troughs called 'flumes', in sections about 3.5 meters long, inclined on trestles. The bottom of the sluice-box is crossed by 'riffle' bars of wood or iron. The smallest of the sluices consists of two such sections. Into the upper one the gravel is thrown, and the lower end is closed by an iron grid to keep back the pebbles and large stones, while the sand, etc, pass through to the lower trough. In this it deposits ite gold and heavy matters behind the riffle bars. In the longer sluices (say 75 meters long) the lower end of the upper section is not blocked, but near it the bottom consists of an iron grating - the 'grizzly'. The large stones are washed forward over the grating, but the sand and fine particles carried by the water fall through it on to the second section of the sluice. In some cases the fine sand, after passing through the first section of the sluice, falls on inclined tables covered witli blankets, rough cloth, or hides witli. the hairy side up, over which it flows in a thin stream. These 'blanket-strakes' serve to arrest and recover the fine gold. In other cases amalgamated copper plates are employed for the same purpose.
Where water is plentiful, 'hydraulic mining' is the cheapest mode of working. Under this system, 'deep leads' (which are alluvial deposits covered over with more recent matter in ancient river beds) and other alluvial deposits are worked by washing down the gravel by means of a powerful jet of water.
In quartz mining - and the case is similar with the hard, solid 'banket' formation of South Africa that contains tlie gold - the ore to be crushed is first passed through a 'stone-breaker' or 'ore crusher', and is further crushed by the 'stamps' or other grinding mill. The ordinary stamp-battery consists, in its lower part, of a cast-iron 'mortar-box', fitted on one or both sides with a fine screen. At the bottom of this box is a row of iron blocks called 'dies', upon which the stamps, or heavy cylindrical cast-iron blocks, are made to rise and fall by means of cams, being thus kept pounding away at the ore in the mortar-box. A stream of water is admitted, and carries the crushed material through the screens. Mercury is fed into the mortar-boxes in small quantities, and much of the gold is retained there on amalgamated copper plates. Slightly inclined amalgamated plates arranged in steps are placed in front of the battery, and over these the crushed orepulp passes slowly, the gold being retained by the amalgamated surfaces. The remaining product, or 'tailings', which may still contain some gold, is then treated either by 'concentration' and the concentrates chlorinated, or the whole is treated by the cyanide process.
For the concentrating process 'vanners' are generally employed. These consist of a slightly sloping table, formed of an endless travelling belt of rubber, which is stretched over rollers and so mounted as to be capable of violent agitation (the vibrations numbering 200 a minute) while moving slowly in an upward direction. The pulp is led on at the higher end, and the flow of water carries the light matters down the slope, the separation being greatly assisted by the shaking movement. The heavy matters only are carried forward by the belt over the higher end, and pass into a box below, being then known as 'concentrates'.
At one time large supplies of gold were obtained from Peru, Bolivia, and other parts of the New World. A rich source of the supply has long been the UralMountains, whence gold is still obtained. An immense increase in the world's production was caused by the discovery of gold in California in 1848, and Australia in 1851, while the South African gold-fields caused a similar increase. It is only since 1886 that the Transvaal became a great gold-producing area, the chief locality being the Witwatersrand.
In Western Australia many mines were opened at the end of the 19th century, and the Yukon district of Canada (Klondike) was also recognized as a gold-field in the 19th century. There are also gold-mines in India that have been worked with great success. Gold has been found in various parts of the United Kingdom, as in Sutherlandshire, Wicklow, and many places in Wales. Research Gold
Goslarite (white vitriol) is hydrated zinc sulphate. It is a rare mineral precipitated from water seeping through the walls of lead mines and is formed by the decomposition of sphalerite. Research Goslarite
Granite is a plutonic, igneous, crystalline, granular rock, consisting generally of quartz, feldspar, and mica, mixed up without regular arrangement of the crystals, and usually of a whitish, greyish, or flesh-red colour. The grains vary in size from that of a pin's head to a mass of almost one meter, but they seldom exceed about two centimetres. When they are of this size, or larger, the granite is said to be 'coarse-grained.'.
Granite is one of the most abundant of the igneous rocks seen at or near the surface of the earth, and was formerly considered as the foundation rock of the globe, or that upon which all sedimentary rocks repose; but it is now known to belong to various ages from the Pre-Cambrian to the Tertiary, the Alps of Europe containing granite of the later age. In Alpine situations it presents the appearance of having broken through the more superficial strata; the beds of other rocks in the vicinity rising towards it at increasing angles of elevation as they approach it. It forms some of the most lofty of the mountain chains of the eastern continent, and the central parts of the principal mountain ranges of Scandinavia, the Alps, the Pyrenees, and the CarpathianMountains are of this rock.
Granite supplies one of the most durable materials for building, as many of the ancient Egyptian monuments testify. It varies much in hardness as well as in colour, in accordance with the nature and proportion of its constituent parts, so that there is much room for care and taste in its selection. Granite in which feldspar predominates is not well adapted for buildings, as it cracks and crumbles down in a few years. The Aberdeen bluish-gray granite is celebrated for its great durability, and also for its beauty. The Peterhead red granite, the hue of which is due to its feldspar being the flesh-coloured potash variety called orthoclase, is highly esteemed for polished work, as columns, pillars, graveyard monuments, etc. Granite in which mica is replaced by hornblende is called syenite; when both mica, and hornblende are present it is called syenitic granite; when talc supplants mica it is called protogene, talcose, or chloritic granite; a mixture of quartz and hypersthene, with scattered flakes of mica, is called hypersthenic granite; and the name of graphic granite, or pegmatite, is given to a variety composed of feldspar and quartz, with a little white mica, so arranged as to produce an irregular laminar structure. When a section of this latter mineral is made at right angles to the alternations of the constituent materials, broken lines resembling Hebrew characters present themselves; hence the name.
Granite abounds in crystallized earthy minerals; and these occur for the most part in veins traversing the mass of the rock. Of these minerals beryl, garnet, and tourmaline are the most abundant. It is not rich in metallic ores. The orientalbasalt, found in rolled masses in the deserts of Egypt, and of which the Egyptians made their statues, is a true granite, its black colour being caused by the presence of hornblende and the black shade of the mica. The oriental red granite chiefly found in Egypt, and of which Pompey's Pillar and Cleopatra's Needles were constructed, is composed of large grains or imperfectly formed crystals of flesh-coloured feldspar, of transparentquartz, and of black hornblende. Research Granite
Granodiorite is a plutonic igneous rock formed from cooling magma in deep zones of mountain belts. Granodiorite is a course-grained intermediate igneous rock comprised mainly of feldspar and quartz, and either pink or white in colour depending upon the proportions of feldspar and quartz. Research Granodiorite
Granulite is a whitish, granular metamorphic rock, consisting of feldspar and quartz intimately mixed. Granulite is formed deep in the Earth's crust at very high temperature and under high pressures. It is sometimes called whitestone or leptynite. Research Granulite
Graphite (also known as Plumbago, Black-lead, and as Wad) is pure carbon with a relative hardness of 2, occurring naturally and often confused with the heavier molybdenite. Graphite occurs not infrequently as a mineral production, and is found in great purity at Borrowdale in Cumberland, and in large quantities in Canada, Sri Lanka, and at Bohemia. Graphite has an iron-grey colour, a metallic lustre, and a granular texture, and is soft and unctuous to the touch. It is formed from organic materials or by the presence of hydrocarbons in a metamorphic region. Graphite may be heated to any extent in close vessels without change and is exceedingly unchangeable in the air and as such has been used in the manufacture of crucibles, as a lubricant when mixed with oils, and as 'lead' for pencils when mixed with clay. Graphite is also used in burnishing iron to protect it from rust, for giving a smooth surface to casting moulds, for coating wax or other impressions of objects designed to be electro-typed, and for counteracting friction between the rubbing surfaces of wood or metal in machinery. Since the start of the 20th century artificial graphite has been produced by the electric furnace. Research Graphite
Graywacke is a metamorphic sandstone in which grains or fragments of various minerals, as quartz and feldspar, or of rocks, as slate and siliceous clay rocks, are embedded in an indurated matrix, which may be siliceous or argillaceous. The colours are grey, red, blue, or some shade of these. The term, as used by the earlier writers, included all the conglomerates, sandstones, and shales of the older formations, when these had been subjected to considerable change. At first it was nearly synonymous with the Silurian strata, these, especially in Scotland, yielding the only genuine graywacke. The term has been little used since the start of the 20th century. Research Graywacke
Green earth (also known as mountain green) is a variety of Glauconite, found in cavities in amygdaloid and other eruptive rock, and used as a pigment by artists. Research Green Earth
Greenockite, named after LordGreenock, is the most common mineral containing cadmium but found in few places and usually as an earthy coating on zinc ores. The largest use of cadmium is for electroplating other metals to form chemical resistant coatings. It has the formulae CdS and a relative hardness of 4. Research Greenockite
Greensand is a variety of sandstone, usually imperfectly consolidated, consisting largely of glauconite, a silicate of iron and potash of a green colour, mixed with sand and a trace of phosphate of lime. Greensand is often called marl, because it is a useful fertilizer. The greensand beds of the American Cretaceous belong mostly to the Upper Cretaceous. Research Greensand
Groppite is a red or brownish-red coloured crystalline mineral with a hardness of 2.5, comprised mainly of aluminium, iron and magnesia found in limestone.
Grossularite (grossular) is a translucentgarnet of a pale green colour like that of the gooseberry. Research Groppite
Gypsum is a common monoclinic mineral distributed in sedimentary rocks, often as thick beds. Gypsum is usually found under beds of rock salt as it's one of the first minerals to crystallize from evaporated saltwaters and is also produced in volcanic areas and in rock veins due to the action of sulphuric acid. Gypsum is used in the production of plaster of Paris. It is chemically a hydrated calcic sulphate and has the formulae CaSO4.2H2O and a relative hardness of 2.
Gypsum is found in a compact state as alabaster, or crystallized as selenite, or in the form of a soft chalky stone, which in a very moderate heat gives out its water of crystallization, and becomes a very fine white powder, extensively used under the name of plaster of Paris. This last is the most common, and is found in great masses near Paris, where it forms the hill of Montmartre, near Aix in Provence, and near Burgos in Spain.
Gypsum may be geologically of any age, but occurs abundantly in the more recent sedimentary formations, and is even now forming, either as a deposit from water holding it in solution, or from the decomposition of iron pyrites when the sulphuric acid combines with lime, or from the action of, sulphurous vapours in volcanic regions on calcareous rocks. When gypsum occurs without water it is called anhydrite, but in its most ordinary state it is combined with water. Research Gypsum
Gyrolite is a white or colourless, glassy-looking secondary mineral. A silicate of calcium, gyrolite is formed through the alteration of pre-existent calciumsilicates and is found mainly in crevices of basalt or as white spherules on a basalt groundmass, rarely larger than 5 cm in diameter. Gyrolite was first discovered in 1851 and was confirmed as a distinct mineral in 1855. Gyrolite aggregates are often accompanied by apophyllite, quartz and zeolites such as analcime. Research Gyrolite
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Rocks & Minerals
Research Gabbronite
