Sulfates, Halides, Phosphates

Sulfate minerals

Hydrous: gypsum, alabaster | Anhydrous: anhydrite, barite, celestite

Halide minerals

Halite, fluorite

Phosphate minerals

Fluor-hydroxy and chlor-apatite, turqouise

Evaporites

Minerals that precipitate when concentration in water reaches a specific temperature reaches their saturation limit.

Order of precipitation first to last

Calcite, gypsum or anhydrite, halite, potassium and magnesium salts

Structural properties of gypsum

Monoclinic, double columns of tacked [SO₄]^-2 tetrahedra are linked to columns of Ca⁺² and water, columns extend along the c-axis, excellent {010} cleavage, flat prismatic crystals, euhedral crystals.

Chemical formula for gypsum

(CaSO₄ * H₂O)

Chemical properties of gypsum

Gypsum is hydrous. If water is removed, anhydrite begins to form where gypsum once was.

General properties of gypsum

Pearly luster, hardness 2, common swallowtail twining

Places of occurrence for gypsum

Low-T hydrothermal, major occurrence in evaporitic deposits, grows in cavities

Structural properties of alabaster

Fine grained massive gypsum

Chemical formula for alabaster

CaSO₄ * H₂O

Chemcial properties for alabaster

Iron impurities make yellow, black or brown veins or patches

Places of occurrence for alabaster

Low pH precipitation, mainly sedimentary with a slightly increased temperature + pressure when forming

Structural properties for anhydrite

Cleavage on (010), (100), (001) planes, individual crystals are rare

Chemical formula for anhydrite

CaSO₄

Chemical properties of anhydrite

Alter to gypsum in humid conditions

General properties of anhydrite

White, gray, or lilac color

Places of occurrence for anhydrite

Typical mineral in evaporate deposits, sedimentary precipitation

Structural properties for barite

Orthorhombic symmetry, rhombic-prismatic or tabular in habit, rosette aggregates are common

Chemcial formula for barite

BaSO₄

Chemical properties of barite

Solid solution with celestite

General properties of barite

High specific gravity/denstiy

Places of occurrence for barite

Med to Low-Temp hydrothermal deposits

Structural properties for celestite

Orthorhombic symmetry, rhombic-prismatic or tabular in habit, common in druses or aggregates

Chemical formula for celestite

SrSO₄

Chemcial properties of celestite

Solid solution with barite

General properties of celestite

Transparent blue color

Places of occurrence for celestite

Hydrothermal, within sedimentary rocks

General properties for halides

Low hardness, high melting point, poor conductor, (some are) soluble

Salt domes

Low density halite NaCl deposits. Intrudes vertically into surrounding rock strata, forming a dome.

Structural properties for halides

Cubic symmetry (CCP), large anions (Cl & F) and metallic cations

Structural properties of halite

Cubic symmetry, {100} cleavage

Chemical formula for halite

NaCl

General properties for halite

Vitreous luster, white or colorless (becomes blue when irradiated with x or gamma rays) or have impurities of Mn (purple), Fe (red), Cu²⁺(green), hardness 2

Structural properties for fluorite

Cubic coordination polyhedron (cube), 1 F for every 4 Ca, isometric, cube or octahedral crystals, perfect {111} cleavage

Chemical formula for fluorite

CaF₂

General properties for fluorite

Vitreous luster, blue, green or violet color, fluorescent in UV, hardness 4

Places of occurrence for flourite

Hydrothermal, common in druses of granite or pegmatites

Structural properties for fluor-hydroxy and chlor-apatite

Hexagonal symmetry, hexagonal prismatic habit

Chemical formula for fluor-hydroxy and chlor-apatite

Ca₅(PO₄)₃ (F, Cl, OH)

General properties for fluor-hydroxy and chlor-apatite

Various colors due to cation substitution, mostly transparent

Places of occurrence for fluor-hydroxy and chlor-apatite

Found in marbles, skarns, and other metamorphic rocks, occurs in igneous rocks and hydrothermal deposits

Structural properties for turquoise

Usually cryptocrystalline

Chemical formula for turquoise

CuAl₆(PO₄)₄(OH)₈ * 4H₂0

General properties for turquoise

Blue to blue-ish green, hardness 6, secondary minerals

Places of occurrence for turquoise

Occurs in veins with altered volcanic rock, often in aggregates