Serpentine

Chemical Formula : (Mg,Fe,Ni)₃Si₂O₅(OH)₄
Hardness : 2.5-5, variable
Cleavage : None
Luster : Waxy to greasy when massive, silky when fibrous.
Color : Green, also yellow, brown, reddish-brown and gray.
Streak : White
Density : 2.5-2.6
Diagnostic Features and Trivia : Serpentine is the main constituent of the rock serpentinite which is the sate rock of California since it is found through out the state, especially in the Franciscan Complex. Serpentine applies to a group of minerals including anitgorite, chrysotile, and lizardite.
Crystal System and Habit : Monoclinic or Orthrhombic; no macroscpoic crystals as it forms unstructured masses except when appearing asbestiform.
Twinning : None
Polymorphs : None
Index of Refraction : variable depending on mineral.
Antigorite : alpha=1.55-1.567; beta=1.56-1.573; gamma=1.56-1.574 Chrysotile : alpha=1.529-1.559; beta=1.53-1.564; gamma=1.537-1.567