last edited: 11/10/17 number of photos: 3
Opal is SiO2.nH2O
hardness: 5.5 to 6.5
Faceted opals are rare because the material is so brittle.
opal, faceted Mexican jelly opals: A B C*
Photos are copyright free for
non-commercial educational uses.
Just credit photos to R.Weller/Cochise College.