# Rocks and Minerals (F-N)

Feldspar
Feldspar refers to a group of minerals containing aluminum and silica. They all show good cleavage in two directions at about 90 degrees. The hardness is about 6 and the specific gravity between 2.5 - 2.8.

Ferberite
Ferberite has the formulae FeWO4 - MnWO4.
It has a relative hardness of 6.
It is the chief ore of tungsten. A rare mineral found usually in pegmatite dikes and high-temperature quartz veins associated with granite.

Ferruginous
Ferruginous refers to containing iron.

Figure-stone
see "Agalmatolit"

Fire-Garnet
see "Pyrope"

Flint
Flint is a compact mineral of fine grained silica. It is a variety of quartz.

Flow banding
Flow banding refers to a structure sometimes found in volcanic rocks where alternating layers of rock have different mineral compositions.

Fluorapatite
Fluorapatite is a common mineral consisting of a mixed phosphate and flouride of calcium. It is a source of phosphorus and was formerly used to make phosphate fertiliser.

Fluorine
Fluorine is a non-metallic element occurring naturally.

Fluorite
Fluorite has the formulae CaF2.
It has a relative hardness of 4.
It is found in veins where it's the main mineral or with metallic ores, especially lead and silver. Common in dolomites and limestone. Associated with many different minerals. Used chiefly as a flux in the making of steel, also for enameling, and it's used in the preparation of hydroflouric acid.

Fluorspar
Fluorspar is a natural mineral containing flourine.

Foliation
Foliation refers to a layered structure present in some metamorphic rocks which results from the segregation of different minerals into roughly parallel layers.

Franklinite
Franklinite has the formulae (Zn,Mn,Fe)(Fe,Mn)2O4
It has a relative hardness of 7.
It is used as an ore of zinc and manganese. With minor exceptions, the mineral is confined to Franklin, New Jersey.

Freibergite
Freibergite is a variety of tetrahedrite containing between 28 and 36 percent silver.

Friable
Friable refers to crumbles or is pulverized easily.

Fulgurite
Fulgurite is a term applied to rocks whose surface has been melted by the action of lightning, and on which the fused material has re-solidified as a kind of thin coat or varnish.

Gabbros
Gabbros are basic rocks solidified under great pressure at considerable depths in the earth's crust. They are coarse-grained and consist of plagioclase felspar with augite. Sometimes the term is widely used to include similar rocks composed of the same felspar with other minerals, and according to the minerals contained they are known as norites, troctolites, eucrites, etc.

Gadolinite
Gadolinite (ytterbite) is a naturally occuring 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.

Galena
Galena (Lead Sulphide) is virtually the only source of lead and an important ore of silver. It has the formulae PbS and a relative hardness of 3.
It is a very common metallic mineral. When found in veins that show a connection to tigneous rocks, it is frequently found with silver minerals. Galena is also found in limestones either as veins or as a replacement deposit.

Gannister
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.

Garnet
Garnet has the formulae A3B2(SiO4)3.
It has a relative hardness of 8.
It is a widely distributed group with several minerals. Found in both metamorphic and igneous rocks. Its chief use is as an inexpensive gem stone. Much is used as an abrasive materal.

Garnierite
Garnierite has the formulae (Ni,Mg)6Si4O10(OH)8.
It has a relative hardness of 4.
It is an ore of nickel. It's probably formed as an alteration of nickel bearing peridotites. Has a nice apple green colour.

Glauberite
Glauberite 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 and a relative hardness of 3.

Glauconite
Glauconite is a mineral of marine origin and found in sedimentary deposits of various kinds. Similar to a mineral called celadonite. 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.

Glaucophane
Glaucophane is a 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.

Gneiss
Gneiss refers to a coarsely foliated (layered) metamorphic rock.

Goethite
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.

Gold
Gold is a rare element with the formulae Au and a relative hardness of 3 occuring 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. Gold in jewellery is measured in carats. 24 carat gold is pure, 22 carat gold is 22 parts gold to 2 parts other metals and so on.

Granite
Granite is a plutonic igneous rock containing a high proportion of silica.

Graphic tellurium
Graphic tellurium is an alternative name for Sylvanite.

Graphite
Graphite is pure carbon with a relative hardness of 2, often confused with the heavier molybdenite. Formed from organic materials or by the presence of hydrocarbons in a metamorphic region. Used in the manufacture of crucibles, as a lubricant when mixed with oils, as 'lead' for pencils when mixed with clay.

Greasy
Greasy refers to a luster of a mineral which appears to be covered with thin coat of oil.

Greenockite
Greenockite 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.

Gypsum
Gypsum is a common mineral distributed in sedimentary rocks, often as thick beds. Usually found under beds of rock salt as it's one of the first minerals to crystallize from evaporated salt waters. Used in the production of plaster of Paris. It has the formulae CaSO4ù2H2O and a relative hardness of 2.

Habit
Habit refers to the physical form of a crystal. It's determined by the shape and relative proportions of the crystal faces.

Haematite
Haematite is an iron ore.

Halides
Halides refers to a group of minerals that are mostly compounds of halogen elements (bromine, chlorine, flourine, iodine). Ex: halite, flourite.

Halite
Halite has the formulae NaCl.
It has a relative hardness of 3.
It is common salt. Tastes salty and exhibits lusterless cubic crystals.

Hardness
Hardness refers to hardness is the resistance of a smooth surface to scratching. It's determined by the binding force of atoms within the crystal structure. Moh's scale of hardness: 1)talc 2)gypsum 3)calcite 4)flourite 5)apatite 6)orthoclase 7)quartz 8)topaz 9)corundum 10)diamond.

Harmotome
Harmotome has the formulae (Ba,K)(Al,Si)2Si6O16ù6H20.
It has a relative hardness of 5.
It occurs mostly in volcanic rocks, especially basalt.

Hausmannite
Hausmannite has the formulae Mn2O4
It has a relative hardness of 6.
It is an excellent ore of manganese.

Hauyne
Hauyne has the formulae (Na,Ca)4-8(Al6Si6)O24(SO4,S)1-2.
It has a relative hardness of 6.
It is of interest to collectors. Occurs in igneous and volcanic rocks.

Hematite
Hematite has the formulae Fe2O3.
It has a relative hardness of 7.
It is the most abundant and important ore or iron. Has been found in enormous deposits in the United States and elsewhere. Many samples are soft as the hematite is sedimentary or weathered iron oxide and the true hardness is not being measured.

Hemimorphite
Hemimorphite has the formulae Zn4Si2O7(OH)2ùH2O.
It has a relative hardness of 5.
It is an ore of zinc. Found in the oxidized regions of zinc deposits.

Heulandite
Heulandite has the formulae (Na,Ca)4-6Al6(Al,Si)4Si26O72ù24H2O.
It has a relative hardness of 4.
It is found in the cavities of basic igneous rocks and often associated with calcite.

Hexagonal
Hexagonal refers to a six sided crystal with hexagonal bases. An unsharpened pencil is a basic example.

Horn Silver
Horn Silver is a native chloride of silver, so called because when fused it assumes a horny appearance.

Hornblende
Hornblende has the formulae (Ca,Na)2-3(Mg,Fe,Al)5(Al,Si)8O22(OH)2
It has a relative hardness of 6.
It is a common member of the amphibole group. Told from pyroxene by cleavage. Found in igneous and metamorphic rocks.

Hydrothermal
Hydrothermal refers to the alteration of minerals or rocks by super-heated mineral rich fluids, usually water, within a crystallizing magma.

Hydrozincite
Hydrozincite has the formulae Zn5(CO3)2(OH)6.
It has a relative hardness of 3.
It is found mainly in deposits associated with smithsonite and occurs as a result of the oxidation of zinc bearing minerals. A major ore of zinc if found in economic quantities.

Ilmenite
Ilmenite has the formulae FeTiO3.
It has a relative hardness of 6.
It has weak magnetism. The major ore of titanium and a common accessory mineral in plutonic rocks. Also in metamorphic rocks. Occurs concentrated in black sand. Associated with magnetite.

Intermediate rock
Intermediate rock refers to an igneous rock that is transitional between acidic and basic rocks. Have a silica content between 54-65%.

Iron
Iron has the formulae Fe and a a relative hardness of 5.
It is is recovered primarily from iron bearing minerals and is recognizable by the oxide coating on its surface (rust).

Isometric
Isometric refers to cubic. Three axis, all the same length and at right angles to each other.

Jade
Jade is a group of glassy silicate minerals including jadetite and nephrite. It is found in shades ranging from white to dark green in Asia.

Jadeite
Jadeite has the formulae Na(Al,Fe+3)Si2O6 and a relative hardness of 7.
It has long been prized in the Orient where it has been used to make beautiful ornaments. Jadeite occurs in large masses in serpentine. Transparent and translucent varieties are called jade.

Jasper
Jasper has the formulae SiO2 and a relative hardness of 7. It is a form of quartz usually coloured red from inclusions of hematite.

Jet
Jet is a soft black mineral.

Kalmuck Agate
see "Cacholong"

Kaolinite
Kaolinite is a hydrous silicate of aluminium with the formulae Al2Si2O5(OH)4 and a relative hardness of 3.
It has a crumbly habit and forms the basis of most clay. Kaolinite is derived from the decomposition of feldspars, particulary aluminum silicates and is one of the most important of the natural industrial substances, used for bricks, ceramics, and many other applications.

Kernite
Kernite has the formulae Na2B4O7ù4H2O and a relative hardness of 3.
It is a major ore of boron. Formed in playa lakes with the boron supplied by thermal springs passing through the underlying volcanic rock.

Kimberlite
Kimberlite is an igneous rock containing very little silica.

Kyanite
Kyanite has the formulae Al2SiO5 and a relative hardness of 7.
It has a different hardness in two directions. An accessory mineral in gneiss and mica schist. It often found with garnet and corundum. Used in the production of refractory porcelains.

Labradorite
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.

Lamellar
Lamellar refers to composed of thin layers, scales, or plates

Lapis lazuli
Lapis lazuli is a blue mineral used in the manufacture of ultramarine pigment.

Lapis ollaris
see "Potstone"

Lapis-lazuli
Lapis-lazuli is a blue stone found in Iraq, Afghanistan and China.

Laumontite
Laumontite has the formulae Ca(Al2Si4)O12ù4H2O.
It has a relative hardness of 4.
It shows a powdery white surface. A form of anaclime (or analcite). Characterized by the fact that it is monoclinic.

Lazulite
Lazulite has the formulae MgAl2(PO4)2(OH)2.
It has a relative hardness of 6.
It is a rare mineral and a minor gem stone. Usually found in quartzites associated with kyanite, andalusite, corundum and rutile. Name derived from the Arabic word for 'heaven' in regard to the mineral's colour.

Lazurite
Lazurite has the formulae (Na,Ca)8(Al,Si)12O24(S,SO4) and a relative hardness of 5.
It is usually shows 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.

Lead Sulphide
see "Galena"

Lenticular
Lenticular refers to having a lens-like shape.

Lepidolite
Lepidolite has the formulae K(Li,Al)3(Si,Al)4O10(F,OH)2 and a relative hardness of 4.
It is a relatively rare mineral 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.

Leucite
Leucite has the formulae KAlSi2O6.
It has a relative hardness of 6.
It is a rather rare mineral occuring only in igneous rocks and usually in recent lavas. 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. From the Greek word for 'white'.

Lime
Lime is the common name of calcium oxide.

Limestone
Limestone is a sedimentary rock composed of calcium carbonate.

Limonite
Limonite is an iron ore found in bog deposits. It has a relative hardness of 5.5.

Luster
Luster 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.

Magma
Magma refers to molten rock beneath the earth's crust. It solidifies to form igneous rocks.

Magnesite
Magnesite has the formulae MgCo3.
It has a relative hardness of 4.
It has been used as an ore of metallic magnesium but the primary source of magnesium is sea water. Is a source of magnesia for industrial chemicals. Commonly found in veins and masses derived from the alteration of serpentine through the action of waters containing carbonic acid.

Magnetite
Magnetite has the formulae Fe3O4.
It has a relative hardness of 7.
It is the richest and most important ore of iron. Found as an accessory mineral in most igneous rocks. Highly magnetic.

Malachite
Malachite has the formulae Ci2(CO3)(OH)2.
It has a relative hardness of 4.
It is a widely distributed copper ore. Found in the oxidized portions of copper veins and is often associated with azurite, cuprite, native copper, iron oxides, and sulphides of copper and iron. Often occurs in copper veins that are found in limestone.

Manganite
Manganite has the formulae MnO(OH).
It has a relative hardness of 4.
It is strongly magnetic. An ore of manganese but seldom found in commercial quantities. Often found in veins associated with granitic igneous rocks. Alters to pyrolusite. Barite and calcite are frequent associates.

Marble
Marble is metamorphosed limestone.

Marcasite
Marcasite has the formulae FeS2.
It has a relative hardness of 7.
It often shows a white colour on a fresh surface. Found in iron metallic veins and frequently with lead and zinc ores. Also found in sedimentary rocks. Marcasite most frequently occurs as a replacement deposit in limestone and often in concretions imbedded in clays, marls, and shales.

Margarite
Margarite has the formulae CaAl2(Al2Si2))O10(OH)2.
It has a relative hardness of 5.
It is a metamorphic mineral associated with staurolite and tourmaline.

Massive
Massive refers to a mineral that does not show any definite external crystal form or consists of poorly defined masses of small crystals.

Mica
Mica refers to a group of silicate minerals having perfect cleavage in one direction and which easily split into thin, elastic, sheets.

Microcrystalline
Microcrystalline refers to a rock in which the crystals are too small to be seen without a microscope.

Microline
Microline has the formulae KAlSi3O8 and a relative hardness of 7. It has the same composition as orthoclase but is distinguished by triclinic twinning (usually requires a microscope). If a feldspar is a deep green it is microline - and sometimes called 'amazon stone'. Told from plagioclase by lack of striations.

Millerite
Millerite has the formulae NiS and a relative hardness of 4. It is the richest ore of nickel but too scattered to be commercially important. Forms at low temperatures often in cavities and as an altered form of other nickel minerals, or as a crystal inclusion in other minerals.

Mimetite
Mimetite is a minor ore of lead and has the formulae Pb5(AsO4)3Cl and a relative hardness of 4.
It is a relatively rare mineral which occurs in the oxidized portions of lead bearing veins.

Mohs
Mohs is a scale of hardness applied to minerals. It ranges from 1 for talc to diamond at 10.

Molybdates
Molybdates refers to a group of minerals in which the molybdate radical (MoO4) is an important constituent. Ex: wulfenite

Molybdenite
Molybdenite has the formulae MoS2 and a relative hardness of 2. It is the main ore of molybdenum. Resembles graphite but has a higher specific gravity and a slight blue tint.

Monazite
Monazite has the formulae (Ca,La,Nd,Th)PO4 and a relative hardness of 6. It is the chief ore of thorium and cerium. Thorium is a radioactive element. It is concentrated in sand due to its durability and high specific gravity. Associated with other heavy minerals such as magnetite, rutile, and zircon.

Monoclinic
Monoclinic refers to a crystal with six faces and three axes of unequal length. Two axes are at right angles to each other and the third is inclined to the plane of the other two. A ream of paper with a long edge sloped at an angle is an example.

Moonstone
see "Adularia"

Mud
Mud is a mixture of clay, sand and organic matter.

Muscovite
Muscovite has the formulae KAl2(AlSi3)O10(OH)2 and a relative hardness of 3. It has extremely perfect cleavage and thin flakes are flexible. Very common. Used for electrical and heat insulation.

Natrolite
Natrolite has the formulae Na2(Al2Si3)O10ù2H2O and a relative hardness of 6. It is of interest to collectors. Found lining cavities in basalts and other lavas. Associated with calcite and zeolites.

Nephiline
Nephiline has the formulae (Na,K)AlSiO4 and a relative hardness of 6. It is confined almost exclusively to the zinc deposits at Franklin, NJ. Associated with franklinite and willemite, often in an intimate mixture.

Niccolite
Niccolite has the formulae NiAs and a relative hardness of 6. It is a minor ore of nickel and often has a copper-like colour.

Nodular
Nodular refers to appearing as or composed of irregular lumps of rock or a mineral.

Copyright 1997,1998 Servile Software Enquiries to Matthew Probert

START PAGE

This site is run as a free public information service