Howlite
Last updated: April 2026
White to gray calcium borosilicate hydroxide with gray-black veining. Widely dyed blue or turquoise-blue and sold as a turquoise imitation — dyed howlite is the most common turquoise simulant in the commercial market. Strong blue LW UV fluorescence is a key natural identification feature.
Howlite has a specific gravity of 2.53 and a refractive index of 1.583–1.608, with a Mohs hardness of 3.5. It is aggregate.
Physical & Optical Properties
Measured with a polariscope, a refractometer, a hydrostatic balance, a Chelsea filter, a UV torch, a loupe, a darkfield loupe and a spectroscope — step-by-step for each.
Through the refractometer
Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.
Key Differentiators
- Natural white/gray color with distinctive gray-black veining resembling spider-web turquoise matrix
- Very low hardness 3.5 — easily scratched by a fingernail or copper coin
- Strong blue LW UV fluorescence (natural undyed material) — diagnostic
- Dyed blue = widely sold as turquoise simulant; acetone definitively removes blue dye
- SG 2.53 lighter than turquoise (2.60–2.85)
Common Simulants
- Magnesite (also dyed as turquoise): Magnesite (H 3.5–4.5, SG ~3.0) is also dyed blue to imitate turquoise. Higher SG than howlite distinguishes them.
Commonly Confused With
Commonly confused with: Turquoise.
Treatments
- Dyed Blue or Turquoise-Blue (primary treatment)
- Dyed Other Colors (red, green, purple, etc.)
- Wax or Resin Impregnation
Related Comparisons
Measurement Guides
Identifying a howlite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Howlite is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →