Howlite, imitation turquoise

• howlite (HOW-lite) is amineral species; monoclinic crystal system; chemical composition Ca2BsSiO9(OH)5
• semi translucent to opaque
• white, often with dark gray and black spiderweb matrix
• commonly dyed blue to imitate turquoise or lapis lazuli 

Identification

• Optic Character: AGG (DR)
• Refractive Index: 1.586-1.605 (+.003), spot reading usually 1.59
• Birefringence: .019 (usually not detectable)
• Pleochroism: none
• Ultraviolet Fluorescence: inert to moderate orange (LW); brownish yellow (SW)
• Absorption Spectra: not diagnostic
• Cause of Color: dye, if colored
• Specific Gravity: 2.58 (-.13)
• Polish Luster: vitreous
• Fracture: granular
• Luster: dull
• Cleavage: none
• Identifying Characteristics: may have spiderweb matrix
• Crystal Habit: massive, compact nodules
• Hardness: 3 to 3% 
• Toughness: fair 

Enhancements

• Method: dyeing

Effect: produces imitation turquoise or imitation lapis lazuli)
Prevalence: occasional
Detection: color does not occur naturally; color filter reaction: pink or red (turquoise gives no reaction; lapis appears dull reddish brown)
Stability: dye will fade
Special Care Instructions: avoid acids, solvents, and prolonged exposure to strong light

Key Separations: howlite from

• turquoise – appearance (texture, possibly color), color filter, SG (possibly), spectrum
• lapis lazuli – appearance (mottling, inclusions), RI, SG (possibly), fluorescence

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