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