Oxides exam 2

manganese nodules

A small (potato-sized) rock that contains manganese and other minerals. Common on parts of the ocean floor.

Corundum

Al2O3 Crystallography: Hexagonal-Trigonal Luster: Vitreous to adamantine Color: Blue-grey, Red (Ruby), Blue (Sapphire) Streak: White (too hard for this test) Hardness: 9 SG: 3.98-4.02 Forms: Hexagonal prisms with basal pinacoid, Twinning: Twins on {101} are common Cleavage: None, uneven to conchoidal fracture Opacity: Opaque to Transparent Gemstones: Ruby and sapphire Star Sapphire: caused by included needles of Rutile. This can be viewed looking down the C-axis

XY2O4 (Spinel) Group:

Crystallizes in Isometric System The unit cell ~ 8 angstroms on a side Includes the 3 Series: 1. Spinel Series 2. Chromite Series and the 3. Magnetite Series

Cuprite

Cu2O Luster: Submetallic - Adamantine Hardness: 3.5-4.0 Color: Ruby red to deep brownish red to nearly black SG: 6.14 Crystallography: Isometric Common Forms: Octahedrons, cubes, and dodecahedrons, massive, granular or earthy Cleavage: Octahedral Cleavage Streak: Brownish red Alteration: Commonly alters to Malachite, Native Cu, Hand Specimen: Deep red color - distinctive,

X2O group

Cuprite Ice

Hematite

Fe2O3 Chemistry; Fe2O3 Crystallography: Hexagonal (Trigonal) Luster: Metallic to earthy Hardness: 5-6 Opacity: Opaque Color: Steel gray for coarse xls. & dull to bright brownish red Streak: Red-brown Cleavage: None, Fracture: It breaks unevenly to conchoidal fracture Key Properties: Red streak Occurrence: Produced by Weathering and Hydrothermal alteration, Precambrian banded Iron formations (Michigan) Associations: Magnetite, Goethite, Limonite

Magnetite

Fe2O4 • Composition: Traces of Titanium (Ti), • Often contains included Ilmenite (FeTiO3) by exsolution as temperature drops • The compositions of coexisting Magnetite and Ilmenite crystals are sensitive to changing temperatures & oxidation state • An important tool in Igneous and Metamorphic Petrology to determine Thermal history and changes in the oxidation state through time Crystallography: Isometric Luster: Dull metallic to splendent Color: Black Streak: Black Cleavage: None, but does show {111} parting on twins SG: 5.18 Hardness: 5.5-6.5 Special Property: Magnetic Alteration: Hematite or goethite

Hercynite

FeAl2O4

Chromite

FeCr2O4 Composition: continuous solid solution from Chromite (FeCr2O4 to MgCr2O4) included Ilmenite (FeTiO3) by exsolution as temperature drops Crystallography: Isometric, mostly octahedrons, granular to massive Luster: Dull metallic to pitchy Color: Black Streak: Brown Cleavage: None, but does show {111} parting on twins SG: 5.09 Hardness: 5.5-6.0 Special Property: Magnetic "Lodestone will pick up metal" Alteration: Hematite or goethite Occurrence: Ultramafic rocks, Layered intrusions Chemistry: Mainly Cr with occasional Traces of Platinum

Iron Hydroxide Minerals

FeO(OH) Limonite Mixtures of Iron oxides and Iron hydroxide minerals +/- clay, silica Yellowish brown to reddish stained rocks is very fine grained Goethite, Lepidocrocite, Hematite, Hand Specimen: Lepidolite med dk yellowish brown, dull to earthy luster Goethite: fibrous to compact accicular parallel to C Crystallography: Orthorhombic

Ilmenite (Hematite group)

FeTiO3 Crystallography: Hexagonal-Trigonal Luster: Metallic - slightly magnetic Color: Black to grey Streak: Black Hardness: 5-6 SG: 4.70-4.79 Forms: tabular xls. Parallel to {001} Twinning: Laminar Twins on {101} are common Cleavage: None, conchoidal to irregular, Opacity: Opaque Composition: Ilmenite-Hematite solid solution above 1050CFe3+, Mg and Mn may substitute for Fe2+ Occurrence: Common accessory in Igneous & Meta Rox.

Occurances of Mn oxides and Hydroxides

Manganese Nodules, Mn dendrites, Desert Varnish

Mineralogical properties of Mn oxides and hydroxides

Mn Oxides & hydroxides Generalized Mineralogical Properties: Color: typically black Streak: Black-dk. Brown SG: ~4-7 Hardness: ~5-7 Opacity: Opaque

Hematite Group

Oxide - X2O3 3 common minerals - Hematite, corundum, Linmenite where Where X = Fe2^3+, or Al2, and Fe2+Ti4+

Cation to oxygen ratio

Oxide minerals are group on this X2O Group: Where X represents Cations of Cu or H: • Cuprite Cu2O: Body-centered cubic with Cu at center • Results in a more covalent bonding • Ice H2O

Spinel - Hercynite

Spinel (MgAl2O4) - Hercynite (FeAl2O4) solid solution series Crystallography: Isometric, Octahedrons common, {111} twins common Luster: Vitreous Color: Red, blue, green, purple Streak: White Cleavage: None, but does show {111} parting on twins SG: 3.55-4.40 (higher values due to increased iron) Hardness: 7.5-8.0 Special Property: transparency and color = gemstones Alteration: resistant to weathering Hand Specimen: Crystal Habit, hardness and color should tip you off Occurrence: Al-rich Metamorphic rocks Associations: Andalusite, Kyanite, Sillimanite, Corundum Also in some marbles, Can be found as detrital sediments (Ceylon)

Rutile

TiO2 Oxide Crystallography: Tetragonal 4/m2/m2/m Luster: Metallic to adamantine Color: Reddish brown to Black Streak: White Hardness: 6-6.5 SG: 4.23-5.5 Forms: Elongate tetragonal prisms, slender, accicular Twinning: Laminar Twins on {101} are common Cleavage: {110} good, {010} fair, conchoidal Opacity: Opaque Composition: TiO2, with some Fe, Ta, Sn, & Nb, V, Cr Occurrence: Common accessory in Igneous & Meta Rocks

Oxide mineral groups

X2O, XO, XY2O4 (Spinel) Group, Hematiite group X2O3, XO2 (Rutile)

Rutile group

XO2 3 common minerals: Rutile, Cassiterite and Pyrolusite Where X = Ti, Sn, Mn

XO group

Zincite (ZnO) hexagonal

Wad

a generic term for mixtures of oxides and hydroxides

Hydrothermal systems

may be primary minerals in viens Manganite and Hausmanite

Mn dendrites

• Branching (Dendritic) mineral growths precipitated from Mn- bearing groundwater along cracks (Joints) • Not composed of pyrolusite (MnO)! • Composed of other Mn oxides & hydroxides

General Properties of Mn oxides and Mn hydroxides

• Mn oxides and hydroxides are fairly common • Typically as small grains, fine-grained masses, and earthy • Commonly intermixed with other Mn oxides & hydroxides, clay, & other mins • Because of these factors, standard methods cannot be applied to Mn oxides

Hydroxide minerals

• Mostly very common minerals • Often the products of weathering and hydration of other minerals • Usually occur as fine-grain aggregates mixed with CLAY Minerals • Both the Hydroxides and the Clay are • Products of chemical weathering and Hydrothermal alteration

Cuprite Occurences

• Occurs in Near-surface • Oxidized zone of Cu-bearing hydrothermal sulfide deposits • Oxidation and alteration of primary Cu sulfides such as: Chalcopyrite CuFeS2 Mineral Associations: Iron Oxides & Iron Hydroxides (Limonite) Malachite, Azurite, Native Cu, black Tenorite (CuO)

Oxide minerals

• Oxides are a Large Group - • Only a few of the Oxide group minerals are abundant • Oxide Minerals have great economic value • Essential Metals for our industrial society from Oxides

Weathering and alteration of Mn minerals

• Primary minerals may weather forming Pseudomorphs • Mn Carbonates (Rhodochrosite) • Mn Silicates (Rhodonite) • Mn Oxides (Manganite)

Desert Varnish

• Red, brown or black coating on exposed rock in a desert setting • Mostly air-transported clay with Mn & Fe oxides