Howlite

Howlite

By Tim Matthews, JD, FGA, GG, DGA,
CEO and President of JTV (retired)
Published: June 2014
Modified: March 2024
Howlite Polished Howlite Rough Howlite Jewelry

Howlite is a basic calcium silico-borate that is used for ornamental and decorative objects. It is whitish or cream in color often with gray or brown veining. It is often mistaken for magnesite, but magnesite will fizz when exposed to dilute HCL and howlite will not. Howlite can be dyed to imitate turquoise..

General Information

Common Name
Howlite
Species
Howlite
Transparency
Semitranslucent - Opaque
Dispersion
Strength: None
Refractive Index
1.586-1.605
Tolerance:(+0.003/-0.003)
Birefringence
0.017- 0.019
Optic Character
Biaxial
Optic Sign
Negative
Polariscope Reaction
Aggregate (AGG), Doubly Refractive (DR)
Fluorescence
SWUV: inert to weak bluish white or brownish yellow; Dyed: brownish yellow
LWUV: Inert to moderate bluish white or orange; Dyed: Inert to orange
CCF Reaction
Dyed blue: pink to red
Pleochroism
None
Hardness
3-3.5
Streak
White
Specific Gravity
2.450-2.590 Typical:2.580
Toughness
Varies
Inclusions
Howlite is often dyed to look like turquoise or lapis lazuli. The stones frequently have a dark gray or black spider web matrix.
Luster
Vitreous, Dull
Stability
Poor
Fracture
Conchoidal to even
Cleavage
None
Chemical Name
Basic calcium silico-borate
Chemical Formula
Ca2B5SiO9(OH)5
Crystal System
Monoclinic
Chemistry Classification
Borate

Howlite Colors

  • Blue Howlite
    Blue
  • Brown Howlite
    Brown
  • Colorless Howlite
    Colorless
  • Green Howlite
    Green
  • White Howlite
    White

Alternate Names

Howlithe, Turquenite, Dyed Howlite

Countries of Origin

Canada; Turkey; Unknown; China; United States of America; Mexico; South Africa; Slovakia; Serbia; United Kingdom of Great Britain and Northern Ireland; Germany; Bolivia (Plurinational State of)

History

Howlite was first reported in 1868 as a silicoborocalcite by Henry How a chemist, geologist, and mineralogist from Nova Scotia. James Dwight Dana later named it Howlite in honor of How.

Care

Normal care for untreated stones. Soluble dilute acids. Avoid harsh chemicals, ultrasonic cleaners, and steaming for stones that have been dyed.