Moss Opal, Dendritic Opal
- opal is a mineral species; amorphous structure; chemical composition SiO2.nH2O (water content usually 3 to 10% by weight, but sometimes as high as 20%)
- opaque
- white, cream body color with moss- like inclusion
- no play-of-color
- moss opal – common opal with inclusions that look like moss
Identification
- Optic Character: SR, ADR common due to strain
- Refractive Index: 1.450 (+.020,-.080). Mexican opal may read as low as 1.37. but it is
- generally 1.42 to 1.43.
- Birefringence: none
- Pleochroism: none
- Absorption Spectra: green – 660 nm, 470 nm cut-off
- Specific Gravity: 2.15 (+.08, -.90)
- Polish Luster: vitreous to resinous
- Fracture: conchoidal to uneven
- Luster: subvitreous to waxy (the latter is more typical of common opal)
- Cleavage: none
- Identifying Characteristics: play-of-color
- Crystal Habit: none, amorphous
- Hardness: 5 to 6 1/2
- Toughness: very poor to fair
Birthstone Designation(s)
- October, 6:00 pm, 14th wedding anniversary
Major Sources: Australia, Brazil, Mexico. Others: Czechoslovakia, Honduras, Indonesia, Poland, Tanzania, US
Stone information is reference from
Gem Reference Guide, Published by GIA. ISBN 0-87311-019-6
Gemstones of the World, Published by Sterling Publishing Co., Inc NY, ISBN 1-4027-4016-6
Encyclopedia of GEMSTONE, Published by ISHINSHA CO., LTD. ISBN 978-986-251-831-1