Crystals
Serpentine
Serpentine subgroup of hydrated sheet silicates Ideal Mg3Si2O5(OH)4 Principal Mg-rich species: antigorite, lizardite, and chrysotile Serpentinite is a rock dominated by serpentine minerals Typical species hardness about 2.5–3.5 Dense lapidary...
Serpentine
Serpentine subgroup of hydrated sheet silicates Ideal Mg3Si2O5(OH)4 Principal Mg-rich species: antigorite, lizardite, and chrysotile Serpentinite is a rock dominated by serpentine minerals Typical species hardness about 2.5–3.5 Dense lapidary...
Selenite
Transparent crystalline variety of gypsum CaSO4·2H2O Monoclinic crystal system Mohs hardness 2 Specific gravity about 2.30–2.33 Perfect sheet-forming cleavage Flexible but inelastic in thin flakes Biaxial positive optical character Evaporites,...
Selenite
Transparent crystalline variety of gypsum CaSO4·2H2O Monoclinic crystal system Mohs hardness 2 Specific gravity about 2.30–2.33 Perfect sheet-forming cleavage Flexible but inelastic in thin flakes Biaxial positive optical character Evaporites,...
Sardonyx
Parallel-banded chalcedony SiO2 Sard red-brown layers with white, gray, or black onyx bands Polycrystalline quartz aggregate with variable moganite Mohs hardness about 6.5–7 Specific gravity commonly about 2.58–2.64 Waxy to...
Sardonyx
Parallel-banded chalcedony SiO2 Sard red-brown layers with white, gray, or black onyx bands Polycrystalline quartz aggregate with variable moganite Mohs hardness about 6.5–7 Specific gravity commonly about 2.58–2.64 Waxy to...
Sapphire
Gem variety of corundum Al2O3 All gem corundum outside the red ruby range Trigonal crystal system Mohs hardness 9 Specific gravity about 3.98–4.10 Uniaxial negative with directional color Metamorphic and...
Sapphire
Gem variety of corundum Al2O3 All gem corundum outside the red ruby range Trigonal crystal system Mohs hardness 9 Specific gravity about 3.98–4.10 Uniaxial negative with directional color Metamorphic and...
Tektite
Tektite • natural terrestrial glass launched from an impact site and deposited across a strewn field Formed during hypervelocity meteorite or asteroid impacts Amorphous glass • no crystal system or...
Tektite
Tektite • natural terrestrial glass launched from an impact site and deposited across a strewn field Formed during hypervelocity meteorite or asteroid impacts Amorphous glass • no crystal system or...
Stromatolite
Stromatolite • laminated microbialite built through repeated surface accretion Microbial mats trap, bind, stabilize, and mineralize sediment Planar, domal, columnar, branching, and conical forms Commonly carbonate; also silicified, dolomitized, phosphatic,...
Stromatolite
Stromatolite • laminated microbialite built through repeated surface accretion Microbial mats trap, bind, stabilize, and mineralize sediment Planar, domal, columnar, branching, and conical forms Commonly carbonate; also silicified, dolomitized, phosphatic,...