Depositional Environments of Mineral Groups 4, 5, 6 & 7

Leucite, nepheline, sodalite

Silica-poor volcanic rocks

Diamond

Altered ultramafic mantle rocks, placer deposits

Sanidine

Volcanic silicic igneous rocks that cooled quickly

Topaz

Hydrothermal veins, contact aureoles adjacent to silicic plutons, late stage igneous crystallization

Chromite

Ultramafic rocks, placers in black sands

Sulfur

Fumaroles, in sed. from bacterial reduction of sulfate minerals

Forsterite

Mafic to ultramafic igneous rocks, metamorphosed sperpentinites and carbonates

Gypsum

Evaporites, deposited by groundwater in sedimentary rocks, alteration product in ore deposits

Anhydrite

Evaporite, secondary precipitated from groundwater, hydrothermal veins, hotsprings

Opal (mineraloid)

Hot springs and low-temperature fluid deposits, replacement of organic material, accumulations of diatoms

Halite and sylvite

Salt flats, evaporites

Natrolite

Cracks, on the walls of cavities in mafic igneous rocks

Montmorillonite and kaolinite

Secondary mineral forming after aluminous silicates

Illite (group)

Weathering and diagenetic environment

Bentonite

Alteration of volcanic ash

Fluorite

Hydrothermal veins, secondary in carbonates with ore minerals, accessory in limestone, accessory in igneous and metamorphic rocks

Pyrolusite

Secondary mineral formed in cracks, coating on surfaces as nodules, in beds

Hematite

Cement in sandstones, sedimentary iron formations, accessory in igneous rocks, hydrothermal veins, altered/oxidized zones in ore deposits

Manganite

Secondary veins

Dolomite

Carbonate sedimentary rocks, hydrothermal veins, alteration after calcite

Barite

Hydrothermal veins, veins in limestone, resdiual in clays

Aragonite

Disseminated in gypsum beds, hot springs deposits, sedimentary iron ore deposits, oxidized zones within ore deposits, cave formations, blueschist metamorphic rocks, shells and other organic carbonates

Calcite

Limestone, marble, cave deposits, veins, cement in sedimentary rocks, shells and skeletal material, weathering

Romanechite

Secondary mineral in near-surface deposits

Limonite

Forms under oxidizing conditions near the surface from iron rich minerals

Bauxite (group/mixture)

Secondary, as a product of intense weathering leading to aluminous soils

Geothite

Secondary mineral found in sediments, gossans, laterites