HOWLITE: California (nodule ~ 3 inches across). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Howlite is always opaque in nodules; it is an abundant material and easy to acquire. Sometimes it contains black, threadlike impurities resembling the veining in turquoise. Howlite is frequently dyed blue to resemble turquoise, and it makes a most convincing simulant. The white material is relatively unexciting in appearance.
| Data | Value |
|---|---|
| Name | Howlite |
| Colors | White. |
| Hardness | 3 - 3.5 |
| Fracture | Even and smooth |
| Cleavage | None |
| Stone Sizes | Spheres up to about 8 inches in diameter have been cut; also seen as cabochons and tumble-polished stones. |
| Formula | Ca2B5SiO9(OH)5 |
| Crystallography | Monoclinic. Crystals tiny; usually nodular masses, chalky or porcellaneous. |
| Refractive Index | 1.583-1.605 |
| Birefringence | 0.022 |
| Luminescence | Brownish yellow in SW; some California material deep orange in LW. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Long, UV-Short |
| Absorption Spectrum | Not diagnostic. |
| Pleochroism | None. |
| Optics | a = 1.583-1.586; β = 1.596-1.598; γ = 1.605. Biaxial (-), 2V large. |
| Optic Sign | Biaxial - |
| Luster | Subvitreous. |
| Specific Gravity | 2.45-2.58 |
| Enhancements | Frequently dyed blue to resemble turquoise. |
| Typical Treatments | Dyeing |
| Transparency | Opaque, except in tiny grains. |
Optics: a = 1.583-1.586; β= 1.596-1.598; γ= 1.605.
Biaxial (-), 2V large.
Occurrence: Microscopic crystals or nodules occur in arid regions or borate deposits.
California: abundant nodules, up to a weight of several hundred pounds, as at Lang in Los Angeles County Also occurs in the Mohave Desert, California. Nova Scotia: small nodules.
Comments: Howlite is always opaque in nodules; it is an abundant material and easy to acquire. Sometimes it contains black, threadlike impurities resembling the veining in turquoise. Howlite is frequently dyed blue to resemble turquoise, and it makes a most convincing simulant. The white material is relatively unexciting in appearance.
Name: After H. How who described a mineral of approximately the same composition.
IGS Newsletter