Crystals
Opal
Hydrated silica mineraloid SiO2·nH2O Amorphous to poorly ordered structure Mohs approximately 5–6.5 Play-of-color by diffraction Fire opal may be precious or common Hydrophane varieties absorb water Solid, boulder, matrix, doublet,...
Opal
Hydrated silica mineraloid SiO2·nH2O Amorphous to poorly ordered structure Mohs approximately 5–6.5 Play-of-color by diffraction Fire opal may be precious or common Hydrophane varieties absorb water Solid, boulder, matrix, doublet,...
Moqui
Iron-oxide sandstone concretions Hematite Fe2O3 Goethite FeO(OH) Quartz-sandstone interiors Navajo Sandstone host Groundwater and redox formation Usually weakly magnetic or nonmagnetic Earth analog for Martian spherules Moqui Marbles: Iron Concretions...
Moqui
Iron-oxide sandstone concretions Hematite Fe2O3 Goethite FeO(OH) Quartz-sandstone interiors Navajo Sandstone host Groundwater and redox formation Usually weakly magnetic or nonmagnetic Earth analog for Martian spherules Moqui Marbles: Iron Concretions...
Moonstone
Feldspar with adularescence Classic orthoclase–albite intergrowth Mohs approximately 6–6.5 Specific gravity approximately 2.56–2.60 Blue, white, or silver floating sheen Peach, cream, gray, and colorless bodies Two cleavage directions near 90...
Moonstone
Feldspar with adularescence Classic orthoclase–albite intergrowth Mohs approximately 6–6.5 Specific gravity approximately 2.56–2.60 Blue, white, or silver floating sheen Peach, cream, gray, and colorless bodies Two cleavage directions near 90...
Obsidian
Natural volcanic glass Typically 70–78% SiO2 Amorphous mineraloid Mohs approximately 5–5.5 Conchoidal fracture Gold and silver sheen Rainbow and fire varieties Snowflake spherulites Hydration, perlite, and archaeology Obsidian: Volcanic Glass...
Obsidian
Natural volcanic glass Typically 70–78% SiO2 Amorphous mineraloid Mohs approximately 5–5.5 Conchoidal fracture Gold and silver sheen Rainbow and fire varieties Snowflake spherulites Hydration, perlite, and archaeology Obsidian: Volcanic Glass...
Lepidolite
Lithium-rich mica series K(Li,Al)3(Si,Al)4O10(F,OH)2 Trioctahedral sheet silicate Typically monoclinic polytypes Perfect basal cleavage Mohs approximately 2.5–4 Lilac, lavender, rose, violet-gray, and silver Late-stage LCT pegmatites Historic source material in rubidium...
Lepidolite
Lithium-rich mica series K(Li,Al)3(Si,Al)4O10(F,OH)2 Trioctahedral sheet silicate Typically monoclinic polytypes Perfect basal cleavage Mohs approximately 2.5–4 Lilac, lavender, rose, violet-gray, and silver Late-stage LCT pegmatites Historic source material in rubidium...
Magnesite
Magnesium carbonate MgCO3 Calcite-group mineral Trigonal crystal system Mohs approximately 3.5–4.5 Perfect rhombohedral cleavage Carbonation of magnesium-rich rock Naturally pale, often dyed Magnesite: The White Carbonate Behind Many Colors Magnesite...
Magnesite
Magnesium carbonate MgCO3 Calcite-group mineral Trigonal crystal system Mohs approximately 3.5–4.5 Perfect rhombohedral cleavage Carbonation of magnesium-rich rock Naturally pale, often dyed Magnesite: The White Carbonate Behind Many Colors Magnesite...