California State Rock - Serpentine
Photo-a-Day 10/9/2012 Bill Stone
The serpentine group describes a group of common rock-forming hydrous magnesium iron phyllosilicate minerals; they may contain minor amounts of other elements including chromium, manganese, cobalt and nickel. In mineralogy and gemology, serpentine may refer to any of 20 varieties belonging to the serpentine group. Owing to admixture, these varieties are not always easy to individualize, and distinctions are not usually made.
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From Bill's Photo-a-Day 2012