Crystals
Feldspar
Feldspar group • framework silicates that dominate many igneous, metamorphic, and sedimentary rocks Major branches: alkali feldspar and plagioclase Principal endmembers: KAlSi3O8, NaAlSi3O8, and CaAl2Si2O8 Mohs 6–6.5 • two cleavages...
Feldspar
Feldspar group • framework silicates that dominate many igneous, metamorphic, and sedimentary rocks Major branches: alkali feldspar and plagioclase Principal endmembers: KAlSi3O8, NaAlSi3O8, and CaAl2Si2O8 Mohs 6–6.5 • two cleavages...
Dinosaur bone
Dinosaur bone • fossil vertebrate tissue preserved through mineral infilling, replacement, or both Body fossil rather than one mineral species Lapidary gembone is commonly silica-rich Iron and manganese create much...
Dinosaur bone
Dinosaur bone • fossil vertebrate tissue preserved through mineral infilling, replacement, or both Body fossil rather than one mineral species Lapidary gembone is commonly silica-rich Iron and manganese create much...
Celestine
Celestine • accepted mineral name; celestite remains a widely used synonym Composition: SrSO4 — strontium sulfate Orthorhombic • barite-group sulfate Mohs 3–3.5 • specific gravity about 3.95–3.97 Perfect basal cleavage...
Celestine
Celestine • accepted mineral name; celestite remains a widely used synonym Composition: SrSO4 — strontium sulfate Orthorhombic • barite-group sulfate Mohs 3–3.5 • specific gravity about 3.95–3.97 Perfect basal cleavage...
Brucite
Brucite • natural magnesium hydroxide • Mg(OH)2 Trigonal structure described in hexagonal axes Perfect basal cleavage • layered octahedral sheets Mohs 2.5–3 • specific gravity about 2.37–2.40 White, green, gray,...
Brucite
Brucite • natural magnesium hydroxide • Mg(OH)2 Trigonal structure described in hexagonal axes Perfect basal cleavage • layered octahedral sheets Mohs 2.5–3 • specific gravity about 2.37–2.40 White, green, gray,...
Blue tiger eye
Falcon’s Eye • Hawk’s Eye • Blue Tiger’s Eye — blue chatoyant quartz with aligned amphibole fibers Principal host: polycrystalline quartz, SiO2 Blue component: comparatively unoxidized riebeckite–crocidolite fibers Optical signature:...
Blue tiger eye
Falcon’s Eye • Hawk’s Eye • Blue Tiger’s Eye — blue chatoyant quartz with aligned amphibole fibers Principal host: polycrystalline quartz, SiO2 Blue component: comparatively unoxidized riebeckite–crocidolite fibers Optical signature:...
Black onyx
Black onyx • straight-banded chalcedony, composed chiefly of microcrystalline quartz with moganite Composition: SiO2 Signature architecture: parallel black, gray, white, or blue-white layers Mohs 6.5–7 • specific gravity about 2.58–2.64...
Black onyx
Black onyx • straight-banded chalcedony, composed chiefly of microcrystalline quartz with moganite Composition: SiO2 Signature architecture: parallel black, gray, white, or blue-white layers Mohs 6.5–7 • specific gravity about 2.58–2.64...