Prehnite
Real mineral · uncommon · Ca₂Al(AlSi₃O₁₀)(OH)₂
A calcium aluminium silicate forming in the vesicles and fractures of basaltic rocks. Often found with zeolites and pectolite as part of low-grade metamorphic mineral assemblages. Its pale green botryoidal masses are distinctive.
Identity
- Formula
- Ca₂Al(AlSi₃O₁₀)(OH)₂
- Chemical class
- silicate
Crystallography
- Crystal system
- orthorhombic
- Habits
- tabular, botryoidal, massive
- Fracture
- uneven
Physical properties
- Mohs hardness
- 6
- Density
- 2.92 g/cm³
- Luster
- vitreous, waxy
- Colors
- pale green, yellow-green, gray, white
- Streak
- white
- Transparency
- translucent, transparent
Geology
- Origins
- hydrothermal, metamorphic
- Host rocks
- basalt, gabbro, schist
- Associated minerals
- zeolite, Pectolite, Calcite, Epidote
- Geography
- South Africa, Australia, China, USA, Mali
Classification
- Rarity
- uncommon
- Gem quality
- Yes
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