monoclinic Simulant turquoise simulant

Dyed Howlite (Turquoise Simulant) (Dyed Howlite (Blue))

Ca2B5SiO9(OH)5 (calcium borosilicate hydroxide; dyed blue to simulate turquoise)

Crystal Structure

CDL Notation

 #! Species: Dyed Howlite (Ca2B5SiO9(OH)5; turquoise simulant)
#! System: Monoclinic (2/m)
#! Habit: Massive; porous; dye concentrates at fractures
monoclinic[2/m]:{010}@1.0 + {110}@0.5 + {001}@0.7

Crystal System monoclinic

Point Group 2/m

Crystal Forms (3)

{010} {110} {001}

Quick Facts

Hardness

3.0

Specific Gravity

2.53

Refractive Index

1.583

Optical Character

Biaxial -

Physical Properties

Crystal Systemmonoclinic

Hardness (Mohs)3.0

Specific Gravity2.53

CleavageNone (but howlite is porous)

FractureConchoidal

LustreSub-vitreous to waxy

Optical Properties

Refractive Index1.583

Birefringence0.022

Optical CharacterBiaxial -

FluorescenceVariable

Origin & Identification

OriginSimulant

First Produced1960

Diagnostic FeaturesDye bleeding at fractures and vugs under 10x loupe; hardness 3-3.5 (scratched by copper coin vs turquoise H 5-6); acetone swab removes blue dye; FTIR borosilicate spectrum vs turquoise phosphate; Chelsea filter reaction differs from natural turquoise; birefringence 0.022 measurable

Colours

Blue to blue-green (dyed); also sold undyed as white howlite

Common Inclusions

Dye bleeding at fractures and vugs (diagnostic under loupe)

Notes

Howlite (Ca2B5SiO9(OH)5) is a natural calcium borosilicate hydroxide mineral; monoclinic 2/m. When dyed blue it closely resembles turquoise. The dye is the simulant aspect. Webster 1962, Journal of Gemmology 8(8):286 (DOI 10.15506/jog.1962.8.8.286) [VERIFIED]: "A New Turquoise Simulant" — first documented dyed howlite as turquoise simulant. Key diagnostics: (1) dye bleeding at fractures/vugs (visible under 10x loupe — natural turquoise shows even colour); (2) hardness 3-3.5 (scratched by copper coin; turquoise H 5-6); (3) acetone swab removes blue dye (natural turquoise colour is intrinsic); (4) FTIR shows borosilicate spectrum (vs phosphate spectrum of turquoise); (5) birefringence 0.022 on flat face (turquoise birefringence too small to observe). Also marketed as "white buffalo turquoise" (undyed) or simply "turquoise" (when dyed). Primarily from California, USA and Canada.