Crystals
Opal
Opal • Hydrated amorphous silica (SiO₂·nH₂O) Structure: silica spheres + water • Amorphous (opal‑A/AG) Mohs ~5–6.5 • SG ~1.98–2.25 Luster: Vitreous to waxy • Fracture: Conchoidal Phenomenon: Play‑of‑color (diffraction) Opal...
Opal
Opal • Hydrated amorphous silica (SiO₂·nH₂O) Structure: silica spheres + water • Amorphous (opal‑A/AG) Mohs ~5–6.5 • SG ~1.98–2.25 Luster: Vitreous to waxy • Fracture: Conchoidal Phenomenon: Play‑of‑color (diffraction) Opal...
Moqui
“Moqui marbles” • Iron‑oxide concretions Host: Navajo Sandstone (Jurassic), SW USA Composition: Hematite (Fe2O3) ± Goethite around quartz sand cores Forms: Spheres • Disks • Doughnuts • Doublets Analog: Compared...
Moqui
“Moqui marbles” • Iron‑oxide concretions Host: Navajo Sandstone (Jurassic), SW USA Composition: Hematite (Fe2O3) ± Goethite around quartz sand cores Forms: Spheres • Disks • Doughnuts • Doublets Analog: Compared...
Moonstone
Moonstone • Feldspar with adularescence Classic species: orthoclase–albite intergrowth (K‑feldspar + Na‑feldspar) Mohs ~6–6.5 • SG ~2.56–2.60 • Cleavage: two directions (good) Optics: RI ~1.518–1.526 • Birefringence ~0.005–0.009 • Phenomena:...
Moonstone
Moonstone • Feldspar with adularescence Classic species: orthoclase–albite intergrowth (K‑feldspar + Na‑feldspar) Mohs ~6–6.5 • SG ~2.56–2.60 • Cleavage: two directions (good) Optics: RI ~1.518–1.526 • Birefringence ~0.005–0.009 • Phenomena:...
Obsidian
Obsidian • Volcanic glass (mineraloid) Chemistry: Silica‑rich melt (rhyolitic) • SiO₂ ~70–78% Mohs ~5–5.5 • SG ~2.3–2.45 Fracture: Conchoidal (razor‑sharp) Phenomena/Varieties: Snowflake • Sheen • Rainbow • Mahogany • “Apache...
Obsidian
Obsidian • Volcanic glass (mineraloid) Chemistry: Silica‑rich melt (rhyolitic) • SiO₂ ~70–78% Mohs ~5–5.5 • SG ~2.3–2.45 Fracture: Conchoidal (razor‑sharp) Phenomena/Varieties: Snowflake • Sheen • Rainbow • Mahogany • “Apache...
Lepidolite
Lepidolite • Lithium‑rich mica (trioctahedral) Approx. formula: K(Li,Al,Rb)3(Al,Si)4O10(F,OH)2 Crystal system: Monoclinic (pseudo‑hexagonal plates) Mohs ~2.5–3 • SG ~2.8–2.9 Cleavage: Perfect on {001} (mica sheets) Palette: Lilac • Lavender • Pink‑rose...
Lepidolite
Lepidolite • Lithium‑rich mica (trioctahedral) Approx. formula: K(Li,Al,Rb)3(Al,Si)4O10(F,OH)2 Crystal system: Monoclinic (pseudo‑hexagonal plates) Mohs ~2.5–3 • SG ~2.8–2.9 Cleavage: Perfect on {001} (mica sheets) Palette: Lilac • Lavender • Pink‑rose...
Magnesite
Magnesite • MgCO₃ — magnesium carbonate (calcite group) Crystal system: Trigonal (rhombohedral) • Cleavage: perfect rhombohedral Mohs: ~3.5–4.5 • SG: ~3.0–3.1 • Luster: vitreous to dull (often chalky) Behavior: fizz...
Magnesite
Magnesite • MgCO₃ — magnesium carbonate (calcite group) Crystal system: Trigonal (rhombohedral) • Cleavage: perfect rhombohedral Mohs: ~3.5–4.5 • SG: ~3.0–3.1 • Luster: vitreous to dull (often chalky) Behavior: fizz...