Crystals
Rhodonite
Manganese silicate CaMn3Mn[Si5O15] Rhodonite-group pyroxenoid Triclinic crystal system Five-tetrahedron silicate-chain repeat Mohs hardness 5.5–6.5 Specific gravity 3.57–3.76 Perfect cleavage in two near-perpendicular directions Rose-pink host with common manganese-oxide alteration Metamorphosed...
Rhodonite
Manganese silicate CaMn3Mn[Si5O15] Rhodonite-group pyroxenoid Triclinic crystal system Five-tetrahedron silicate-chain repeat Mohs hardness 5.5–6.5 Specific gravity 3.57–3.76 Perfect cleavage in two near-perpendicular directions Rose-pink host with common manganese-oxide alteration Metamorphosed...
Rhodochrosite
Manganese carbonate MnCO3 Calcite group · trigonal symmetry Rhombohedra, scalenohedra, stalactites, and botryoidal masses Mohs hardness 3.5–4 Specific gravity about 3.7 Perfect rhombohedral cleavage Uniaxial negative with very high birefringence...
Rhodochrosite
Manganese carbonate MnCO3 Calcite group · trigonal symmetry Rhombohedra, scalenohedra, stalactites, and botryoidal masses Mohs hardness 3.5–4 Specific gravity about 3.7 Perfect rhombohedral cleavage Uniaxial negative with very high birefringence...
Quartz
Silicon dioxide SiO2 Trigonal crystal system at ordinary conditions Hexagonal prisms with rhombohedral terminations Mohs hardness 7 Specific gravity about 2.65 Uniaxial positive and optically active Piezoelectric and widely used...
Quartz
Silicon dioxide SiO2 Trigonal crystal system at ordinary conditions Hexagonal prisms with rhombohedral terminations Mohs hardness 7 Specific gravity about 2.65 Uniaxial positive and optically active Piezoelectric and widely used...
Pyrite
Iron disulfide FeS2 Cubic crystal system Cubes, pyritohedra, octahedra, and combinations Mohs hardness 6–6.5 Specific gravity about 5.0 Metallic brass-yellow luster Greenish-black to brownish-black streak Hydrothermal, sedimentary, igneous, and metamorphic...
Pyrite
Iron disulfide FeS2 Cubic crystal system Cubes, pyritohedra, octahedra, and combinations Mohs hardness 6–6.5 Specific gravity about 5.0 Metallic brass-yellow luster Greenish-black to brownish-black streak Hydrothermal, sedimentary, igneous, and metamorphic...
Prehnite
Calcium–aluminum silicate hydroxide Ca2Al2Si3O10(OH)2 Orthorhombic crystal system Botryoidal, fanlike, reniform, and stalactitic habits Mohs hardness 6–6.5 Specific gravity 2.80–2.95 Biaxial positive optical character Mafic-rock cavities and low-grade metamorphism Often associated...
Prehnite
Calcium–aluminum silicate hydroxide Ca2Al2Si3O10(OH)2 Orthorhombic crystal system Botryoidal, fanlike, reniform, and stalactitic habits Mohs hardness 6–6.5 Specific gravity 2.80–2.95 Biaxial positive optical character Mafic-rock cavities and low-grade metamorphism Often associated...
Porphyry
Igneous rock texture Phenocrysts in fine groundmass Felsic to mafic compositions Volcanic and shallow intrusive Quartz, feldspar, amphibole, pyroxene, or olivine Two-stage model with complex crystal histories Imperial purple porphyry...
Porphyry
Igneous rock texture Phenocrysts in fine groundmass Felsic to mafic compositions Volcanic and shallow intrusive Quartz, feldspar, amphibole, pyroxene, or olivine Two-stage model with complex crystal histories Imperial purple porphyry...