Oxide & Hydroxide Minerals

Periclase Group

• Periclase - MgO , colorless to grey to yellow brown , H = 5.5 , density = 3.58 , rare mineral found in calcite granulite associated with brucite and magnesite
• Zincite - ZnO , deep red color , massive habit , H = 4 , density = 5.68 , perfect cleavage , orange yellow streak , subadamantine luster ; association with willimite (green) , calcite (white) and franklinite (black)

Spinel Group

• Spinel - MgAlO , color varies but commonly black to brown , octahedral crystals or massive , H = 7.5 to 8 , density = 3.58 ,high temperature metamorphic or igneous mineral , poor cleavage , vitreous luster , white streak
• Magnetite - FeFeO , massive to octahedral crystals , highly magnetic , black color and streak , H = 5.5 to 6.5 , octahedral parting , metallic luster , density = 5.2
• Chromite - FeCrO , massive granular to compact , black color , brown streak , H = 5.5 , density = 5.09 , submetallic luster , sometimes slightly magnetic , found in ultrabasic rocks such as serpentines and peridotites, no cleavage
• Gahnite - ZnAlO , green color , grey streak , octahedral or massive habit , H = 8 , found around metamorphosed zinc sulfide deposits , vitreous luster
• Franklinite - (Zn,Mn,Fe)(Fe,Mn)O , black to brown black color , massive or octahedral crystals , red brown streak , weakly magnetic , H = 5.5 to 6.5 , conchoidal fracture , metallic luster , density = 5.07 to 5.22 ; associated with zincite , willimite and calcite
• Hausmanite - MnMnO , massive to granular , H = 5.5 , density = 4.84 , brown black color , brown streak , contact metamorphic or hydrothermal deposit mineral
• Chrysoberyl - BeAlO , green to yellow green color , white streak , H = 8.5 , density = 3.75 , tabular crystals often cyclic twinnes , found in pegmatites and mica schists

Hematite Group

• Hematite - FeO , color varies from red to brown to grey to silver , red brown streak , metallic to earthy luster , H = 5 to 6 softer in earthy varieties , flat platy to massive habit , no cleavage , density = 5.2 to 5.3
• Corundum - AlO , color varies typically brown , tabular to barrel shaped crystals , H = 9 , density = 4 to 4.1 , high grade metamorphic rocks , igneous rocks and pegmatites , adamantine luster
• Ilmenite - FeTiO , black color and streak , submetallic luster , may be slightly magnetic , conchoidal fracture , H = 5 to 6 , density = 4.7

Romancherite Group

• Romancherite - (Ba,HO)MnO , Iron black to steel grey color , brown black to black streak , massive to botryoidal habit , H = 5 to 6 , density 4.7 , submetallic luster ; associated with pyrolusite , goethite , and hausmanite

Rutile Group

• Rutile - TiO , color varies from red-brown to black to golden yellow , pale brown to white streak , prismatic dipyramidal to acicular crystals also massive granular , H = 6 to 6.5 , perfect cleavage , metallic luster , density = 4.3
• Pyrolusite - MnO , black color , blue black streak , dendritic habit crusts or coatings , H = 6 to 6.5 , metallic to earthy luster , density = 4.4 to 5 , poor cleavage
• Cassiterite - short prismatic to botryoidal habit , red brown to black brown color , grey white to brown streak , H = 6 to 7 , density = 7 , found in hydrothermal veins and metasomatic deposits , conchoidal fracture , adamantine luster

Hydroxides

• Bauxite - , actually three separate crystals.... diaspore , boehmite , gibbsite , Pisolitic aggregates , white to reddish-white color , density = 3 , vitreous luster, ore of aliminum ; diaspore - AlO(OH) , H = 6.5 to 7 , good cleavage ; boehmite - AlO(OH) , H = 2.5 to 3 , perfect cleavage ; gibbsite - Al(OH) , H = 2.5 to 3 , perfect cleavage
• Goethite - FeO(OH) , black to yellow color , H = 5 to 5.5 less in earthy varieties , brownish yellow to brown streak , metallic to earthy luster , botryoidal to massive habit (crystals to small to see)