13.3" Green Prehnite Crystal Cluster on Rock - Morocco
This is a specimen of green prehnite still on the rock it was found on, collected in Morocco. The prehnite crystals formed in seemingly striated patterns, all bunched up next to each other with rectangular, "bowtie" crystal structures.
Prehnite is a calcium aluminum silicate with the chemical composition Ca2Al(AlSi3O10)(OH)2. It generally occurs as volcanic cavity infillings, and typically is a shade between yellow and green, however colorless and blue specimens are not unheard of.