Prehnite is an inosilicate of calcium and aluminium with the formula: Ca₂Al(OH)₂. Limited Fe³⁺ substitutes for aluminium in the structure.
Color: Green
Luster: Vitreous, Waxy
Crystal system: Orthorhombic crystal system
Chemical formula: Ca₂Al₂Si₃O₁₂ (OH)
Hardness (Mohs hardness scale): 6 – 6.5
Transparency: Translucent
Refractive index: 1.61 – 1.64
Epidote is a calcium aluminium iron sorosilicate mineral.
Cleavage: perfect and, imperfect
Streak: Greyish white
Color: Pistachio-green, yellow-green, greenish black, brownish-green, green, black
Specific gravity: 3.38-3.49
Luster: Vitreous to resinous
Crystal system: Monoclinic
