Pearl

A pearl is a hard, glistening object produced within the soft tissue of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of... Wikipedia

• Category:  Carbonate mineral, protein
• Formula, (repeating unit):  Calcium carbonate, CaCO 3, Conchiolin
• Strunz classification:  05.8
• Crystal system:  Orthorhombic
• Color:  White, pink, silver, cream, brown, green, blue, black, yellow, orange, red, gold, purple, iridescent
• Cleavage:  None
• Fracture:  Uneven, various
• Mohs scale hardness:  2.5–4.5
• Streak:  White
• Specific gravity:  2.60–2.85
• Refractive index:  Common pearl: 1.52-1.66, Black pearl: 1.53-1.69
• Birefringence:  0.156
• Pleochroism:  Absent
• Dispersion:  None
• Ultraviolet fluorescence:  White pearls: light blue to light yellow, Yellow and golden pearls: yellow-green, greenish brown to dark brown, Black pearls: commonly pink to orange-red
• Data source:  DuckDuckGo