Oxides – Generally Ore Minerals
Hematite Group – X2O3 Type
Ruby
Sapphire
Corundum - Al2O3
Hexagonal, tabular or prismatic xstals
Color – brown, gray, red or blue; sapphire or ruby
H = 9; adamantine to vitreous luster; S. G. = 4.02
Emery – black granular corundum mixed w/magnetite,
hematite
Occurrence: common accessory mineral in some metamorphic
and igneous rocks
Oxides – Generally Ore Minerals
Hematite Group – X2O3 Type
Specular
Botryoidal habit
Hematite - Fe2O3
Hexagonal, reddish-brown to black
Red oolitic hematite – dull luster, Specular hematite – metallic luster
Streak – light to dark red
H = 6; S. G. = 5
Occurrence: widespread, most abundant ore of Fe; contact
metamorphic deposits, granites, sedimentary rocks
In U.S., Precambrian Fe ore deposits grouped around S and NW
shores of Lake Superior in MI, WI, MN
Oxides – Generally Ore Minerals
Hematite Group – X2O3 Type
Ilmenite - FeTiO3
Hexagonal, xstals tabular w/ prominent basal planes; massive
Color – black; submetallic to metallic luster
H = 5.5-6; S. G. = 4.7
Weakly magnetic
Occurrence: common accessory mineral in igneous rocks;
associated w/magnetite
Constituent of black sands associated w/magnetite, zircon, rutile
and monazite (ZTR index)
Mined at Tahawus, NY – Ti ore
Oxides – Generally Ore Minerals
Rutile Group – XO2 Type
Rutile – TiO2
Tetragonal, prismatic xstals w/ striated prism faces; elbow twins;
slender acicular xstals in quartz, massive
Color – red to black; adamantine to submetallic luster
H = 6-6.5; S. G. = 4.2
Streak = pale brown
Occurrence: granites, pegmatites, accessory in metamorphic
rocks
Constituent of black sands associated w/magnetite, zircon, and
monazite (ZTR index)
Oxides – Generally Ore Minerals
Rutile Group – XO2 Type
Cassiterite – SnO2
Tetragonal, prismatic xstals w/ dipyramids; elbow twins;
usually massive granular
Color – brown to black; adamantine to dull luster
H = 6-7; S. G. = 7
Streak = white; chief ore of tin (Sn)
Occurrence: hydrothermal veins near granites, rolled pebbles in
placer deposits called “stream tin”
Associated with molybdenite and arsenopyrite
Oxides – Generally Ore Minerals
Spinel Group – XY2O4 Type
Spinel – MgAl2O4
Isometric, octahedral xstals
Color – variable, ruby spinel in our collection; vitreous luster
H = 8; S. G. = 3.5 - 4.1
Streak = white
Occurrence: common high T mineral in contact metamorphic
limestones; associated with phlogopite, pyrrhotite and graphite
Accessory mineral in mafic and ultramafic igneous rocks,
peridotite and dunite
Oxides – Generally Ore Minerals
Spinel Group – XY2O4 Type
Chromite – FeCr2O4
Isometric; massive granular habit
Color – black; metallic luster
H = 5.5; S. G. = 4.6
Streak = dark brown
Only ore of Cr; additive to steel, strategic metal
Occurrence: accessory mineral in ultramafic igneous rocks,
peridotite and serpentinite
Oxides – Generally Ore Minerals
Spinel Group – XY2O4 Type
Magnetite – Fe3O4
Isometric; octahedral xstals, usually massive granular
Color – black; metallic luster; Streak = black
H = 6; S. G. = 5.2; Strongly magnetic
Fe ore
Occurrence: accessory mineral in igneous rocks, chlorite schists
(greenschists)
Inverse spinel structure: Y(XY)O4 or Fe3+(Fe3+Fe2+)O4
Carbonates – contain (CO3)2-
Calcite – CaCO3
Hexagonal - trigonal; rhombohedral and scalenohedral xstals,
and massive
Color – white, colorless, blue, pink, yellow; vitreous luster
Effervesces freely w/cold HCl; rhombohedral cleavage
H = 3; S. G. = 2.7; twinning common
Occurrence: common rock-forming mineral in limestone, marbles,
chalk; cave deposits called travertine; onyx is banded calcite
Used in manufacture of cements and lime for mortars, building
stone
Carbonates – contain (CO3)2-
Aragonite – CaCO3 (polymorph of calcite)
Orthorhomic; tabular or twinned xstals, stalactitic
Color – white; vitreous luster; pearly layer in shells
Effervesces freely w/cold HCl; Lacks rhombohedral cleavage
H = 3.5-4; S. G. = 2.9;
Occurrence: warm water precipitate,deposited by hot springs as
travertine, e.g., Mammoth Springs, Yellowstone
Associated w/gypsum and Fe ore deposits – forms resemble coral
called flos ferri
High P metamorphic rocks, e.g., Franciscan Fm., CA
Carbonates – contain (CO3)2-
Dolomite – CaMg(CO3)2
Hexagonal; rhombohedral xstals w/curved faces; saddle-shaped
Color – pink to beige; vitreous luster;
Must be powdered to react w/cold HCl; rhombohedral cleavage
H = 3.5-4; S. G. = 2.9;
Occurrence: composes dolomite rock of secondary origin; Ca2+
replaced by Mg2+
Hydrothermal veins – Mississippi Valley deposits w/sulfide ores
Hydrous Carbonates – contain (CO3)2- and (OH)2
Malachite and Azurite
Malachite – Cu2CO3(OH)2
Monoclinic; radiating fibers forming botryoidal or stalactitic masses
Color – bright green; vitreous to earthy luster; light green streak
Effervesces w/cold HCl;
H = 3.5-4; S. G. = 3.7-4;
Occurrence: widely distributed Cu mineral associated w/Cu ore
deposits and azurite
Used as ornamental and gem stone
Hydrous Carbonates – contain (CO3)2- and (OH)2
Malachite and Azurite
Azurite – Cu3(CO3)2(OH)2
Monoclinic; generally massive; forms as crust on other Cu minerals
Color – bright blue; earthy luster; blue streak
Effervesces w/cold HCl;
H = 3.5-4; S. G. = 3.8
Occurrence: secondary Cu mineral formed by alteration of Cu ore
deposits; associated w/malachite but less common
Phosphates – contain (PO4)3-
Apatite – Ca5(PO4)3(F,Cl,OH)
Hexagonal; long prismatic xstals w/dipyramids or basal parting
Color – green to brown; resinous to vitreous luster
H = 5; S. G. = 3.2
Fluorapatite – most common
Occurrence: widespread accessory mineral in all rock types and
pegmatite veins
Phosphate materials of bones and teeth; collophane is massive
apatite – fossil bones, phosphate rock
Dr. R-T’s favorite mineral!