Crystals
Amber
Fossil resin Organic gem rather than a mineral Amorphous polymeric material Mohs approximately 2–2.5 Specific gravity approximately 1.05–1.10 Plant, fungal, and arthropod inclusions Variable fluorescence Natural, heated, clarified, pressed, or...
Amber
Fossil resin Organic gem rather than a mineral Amorphous polymeric material Mohs approximately 2–2.5 Specific gravity approximately 1.05–1.10 Plant, fungal, and arthropod inclusions Variable fluorescence Natural, heated, clarified, pressed, or...
Onyx
Banded chalcedony SiO2 Parallel black-and-white layers Sardonyx: brown-red and pale bands Mohs approximately 6.5–7 Waxy to vitreous luster Classic cameo and intaglio material Commercial black material is often treated Distinct...
Onyx
Banded chalcedony SiO2 Parallel black-and-white layers Sardonyx: brown-red and pale bands Mohs approximately 6.5–7 Waxy to vitreous luster Classic cameo and intaglio material Commercial black material is often treated Distinct...
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...