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Labradorite has the formulae (Na,Ca)AlSi3O8 and a relative hardness of 6. It is one of the plagioclase feldspars, also known as soda-lime feldspars. Others in the grouping are: albite, oligoclase, andesine, bytownite, and anorthite.
Labradorite often has a beautiful display of colours. The name is derived from the locality of Labrador.
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A laccolith (or laccolite) is a dome of igneous rock between two layers of older sedimentary rock. They are formed by the intrusion of magma, which forces the overlying strata into a dome.
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Lamellar refers to composed of thin layers, scales, or plates
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Lanarkite is a mineral consisting of sulphate of lead, occurring either massive or in long slender prisms, of a greenish-white or grey colour.
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Lanthanite is hydrous carbonate of lanthanum, found in tabular white crystals.
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Lapis lazuli is a blue mineral used in the manufacture of ultramarine pigment.
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Laumontite, named after its discoverer, Dr Laumont, is a form of anaclime (or analcite) with a powdery white surface. It is characterised by the fact that it is monoclinic. It has the formulae Ca(Al2Si4)O12ù4H2O and a relative hardness of 4. Exposed to the air, it loses water, becomes opaque, and crumbles.
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Laurite is a rare sulphide of osmium and ruthenium found with platinum in Borneo and Oregon.
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Lava is the molten material expelled by a volcano. It cools to form igneous rock.
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Lazulite is a rare mineral and a minor gem stone of a light indigo-blue colour, occurring in small masses, or in monoclinic crystals. It is a hydrous phosphate of alumina and magnesia. It is usually found in quartzites associated with kyanite, andalusite, corundum and rutile. It has the formulae MgAl2(PO4)2(OH)2 and a relative hardness of 6.
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Lazurite has the formulae (Na,Ca)8(Al,Si)12O24(S,SO4) and a relative hardness of 5. It is usually a deep blue colour, the greenish variety is called lapis lazuli and is very rare. Lazurite is found in metamorphic limestones associated with calcite and pyrite.
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Leadhillite, so called from having been first found at Leadhills, Scotland, is a transparent to translucent mineral of a yellowish or greenish white colour, consisting of the sulphate and carbonate of lead. It is a secondary mineral confirmed as a distinct species in 1832 and formed in the oxidation zones of lead deposits where it is commonly associated with anglesite, cerussite, chalcosite, dioptase, galena, linarite, malachite, silver, willemite and wulfenite.
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Lenticular refers to having a lens-like shape.
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Lepidocrocite is a secondary mineral that is generally found in association with goethite and other iron-bearing minerals, especially hematite, ilmenite, limonite, magnetite, pyrite and siderite. Lepidocrocite is very similar to goethite, the two having the same chemical formula but differing in specific gravity - due to the different manner in which they formed - lepidocrocite being heavier.
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Lepidolite is a relatively rare species of mica, of a lilac or rose-violet colour, found in pegmatic dikes and usually associated with lithium bearing minerals such as pink and green tourmaline. Often found intergrown with muscovite. Used as a source of lithium and it's used in the manufacture of heat resistant glass. It has the formulae K(Li,Al)3(Si,Al)4O10(F,OH)2 and a relative hardness of 4.
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Lepidomelaneis an iron-potash mica, of a raven-black colour, usually found in granitic rocks in small six- sided tables, or as an aggregation of minute opaque scales.
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Leucite is a rather rare mineral occurring only in igneous rocks and usually in recent lavas. It is found in rocks where the amount of silica in the magma was not sufficient to form feldspar. It is not found, therefore, in rocks that contain quartz. It's name is derived from the Greek word for ' white'. It has the formulae KAlSi2O6 and a relative hardness of 6.
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Leucophane or leucophanite is a mineral of a greenish yellow colour. It is a silicate of glucina, lime, and soda with fluorine.
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Leucopyrite is a mineral of a colour between white and steel-grey, with a metallic lustre, and consisting chiefly of arsenic and iron.
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Leucoxene is a nearly opaque white mineral, in part identical with titanite, observed in some igneous rocks as the result of the alteration of titanic iron.
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Levyne, named after the English mineralogist Levy, is a whitish, reddish, or yellowish, transparent or translucent mineral, allied to chabazite.
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Lherzolite, named after Lherz in the Pyrenees is an igneous rock consisting largely of chrysolite, with pyroxene and picotite (a variety of spinel containing chromium).
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Libethenite, named after Libethen, in Hungary, where it was first found, is a rare secondary mineral of an olive-green or deep-green colour, commonly occurring in orthorhombic crystals. It is a hydrous phosphate of copper formed by metasomatism in deeply weathered, highly concentrated copper sulphide ore bodies. Libethenite was confirmed as a distinct species in 1823.
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Lignite (brown coal, wood coal) is a mineral coal closely related to jet, retaining the texture of the wood from which it was formed, and burning with an empyreumatic odour. It is of more recent origin than the anthracite and bituminous coal of the proper coal series, and often contains untransformed woody material.
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Lime is the common name of calcium oxide, and second only to sulphuric acid is the most widely used chemical in industry, being extensively used in the agricultural, building and chemical industries.
Lime is an alkali and is chiefly used in chemistry and agriculture for neutralizing acids - in agriculture to reduce the acidity of soil. Lime has long been derived from chalk and oyster shells.
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Limestone is a sedimentary rock composed of calcium carbonate. It is used as a source of cement in the building industry and for blackboard chalk.
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Limonite is the hydrated oxide of iron. It never occurs crystallised, but in fibrous, earthy, stalactitic mammillary, porous, or concretionary masses, and often as pseudomorphs formed by the weathering of other minerals such as pyrites or marcasite. It is black or brown in colour and the streak or fine powder is yellow, distinguishing it from haematite. It has a relative hardness of 5. 5. Impure limonite is found in moorland clay soils and also in meadows and bogs in spongy nodules, and is hence known as bog iron ore. In fresh-water lakes it is often deposited as a brownish slime by the action of plants on the ferrous carbonate and in Sweden and Norway this lake ore is periodically collected by raking the bottom of the shallow pools. Earthy
limonite, or limonite mixed with clay is known as yellow ochre.
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Linarite is a hydrous sulphate of lead and copper occurring in bright blue monoclinic crystals. Linarite is a rare secondary mineral formed in lead and copper veins that have been altered by the action of water and other circulating fluids. It is most often associated with anglesite, brochantite, cerussite, chalcanthite, chalcopyrite, galena and malachite. Linarite is named after the place where it was first discovered, Linares in Spain. It was confirmed as a distinct species in 1839. It has a relative hardness of 2.5 and is fairly heavy.
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Liroconite is a hydrated arsenate of copper, occurring in obtuse pyramidal crystals of a sky-blue or verdigris-green colour.
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Litharge is a red lead oxide mineral, dimorphous with massicot, and is often found as a crust enveloping an inner core of massicot in a rock base. Linarite is amphoteric - it dissolves equally well in acids and alkalis, and was formerly used to prepare lead salts and plumbates to make rust-resistant paints.
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Lithiophilite is a phosphate of manganese and lithium; a variety of triphylite.
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Lithographic limestone is a compact, fine-grained limestone, obtained largely from the Lias and Oolite, especially of Bavaria, and extensively used in lithography.
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Lithomarge is a compact variety of kaolin or of clay, soft, unctuous, and friable. It is usually white or grey and is particularly found in Cornwall, Germany and America.
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Lithophyse is a spherulitic cavity often with concentric chambers, observed in some volcanic rocks, as in rhyolitic lavas. It is supposed to be produced by expanding gas, hence the name.
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Lizard stone is a kind of serpentine from near Lizard Point, Cornwall, England, used for ornamental purposes.
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Loellingite (Lollingite) is a tin-white coloured arsenide of iron, isomorphous with arsenopyrite. Loellingite was confirmed as a distinct species of mineral in 1845 and named after the place where it was discovered - Lolling in Austria. The arsenic in loellingite is often partially replaced by cobalt, nickel or sulphur, when it is completely replaced by cobalt a new mineral is formed - safflorite.
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Lucullite, named after Lucullus, a Roman consul, famous for his great wealth and Luxury, is a variety of black limestone, often polished for ornamental purposes.
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Ludlamite is a mineral occurring in small, green, transparent, monoclinic crystals. It is a hydrous phosphate of iron.
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Ludwigite, named after the chemist Ernst Ludwig, is a rare mineral, a borate of iron and magnesia, occurring in fibrous masses of a blackish-green colour.
Ludwigite forms at high temperatures in contact zones of metamorphic rocks and is found mainly in association with cassiterite and iron ores. It has a relative hardness of 5.
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Lumachel is a greyish brown limestone, containing fossil shells, which reflect a beautiful play of colours. It is also called fire marble, from its fiery reflections.
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Lustre refers to the general look of a mineral in reflected light. Minerals are divided into two types: metallic and non-metallic. There's no clear dividing line between the two. In general, non- metallic minerals will transmit light through a thin edge, are light coloured, and will have a light or colourless streak. Non- metallic minerals are further described as: vitreous, resinous, pearly, greasy, silky, adamantine.
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Luxullianite is a kind of granite from Luxullian, Cornwall, characterized by the presence of radiating groups of minute tourmaline crystals.
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Abbreviations
Rocks & Minerals
