Impression Stone
- calcite (KAL-site) is a mineral species; hexagonal (trigonal) crystal system; chemical composition CaCO3
- opaque
- pale green with brown stripe
- onyx marble – banded marble
Identification
- Optic Character: DR, uniaxial negative; AGG
- Refractive Index: 1.486-1.658
- Birefringence: .172
- Dispersion: .017
- Pleochroism: none to weak
- Ultraviolet Fluorescence: variable
- Absorption Spectra: any lines seen are due to impurities or dye
- Specific Gravity: 2.70 (+-.05)
- Cause of Color: various impurities
- Polish Luster: vitreous to greasy
- Fracture: granular to uneven to splintery
- Luster: dull (on aggregates) to subvitreous
- Cleavage: perfect in three directions; often obscured in aggregates
- Identifying Characteristics: strong doubling in transparent varieties; high spot birefringence on aggregates
- Hardness: 3
- Toughness: poor in single crystals, fair to good in aggregates
Enhancements
- Method: dyeing
Effect: adds color to marble varieties
Prevalence: common
Detection: magnification, spectrum, color filter
Stability: dyes may fade
Special Care Instructions: avoid solvents, heat, and prolonged exposure to strong light
- Method: paraffin or plastic impregnation
Effect: improves the appearance of the polish
Prevalence: common
Detection: hot point
Stability: paraffin may discolor
Special Care Instructions: avoid solvents and heat
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
