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Lawsonite
Current inventory:  0 gems
 

Chemistry:  CaAl₂Si₂O₇(OH)₂·(H₂O)  
[Hydrated Calcium Aluminum Silicate]

Discovered in 1895;   IMA status: Valid (pre-IMA; Grandfathered).
Lawsonite is named for Professor Andrew Cowper Lawson (1861-1952), Scottish-American geologist, University of California, Berkeley, California, USA.

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/C.10-10

Nickel-Strunz 10th Ed. ID:

9.BE.05

9 : SILICATES (Germanates)
B : Sorosilicates
E : Si₂O₇ groups, with additional anions; cations in octahedral [6] and greater coordination

Related to:

Lawsonite - Ilvaite Series. Dimorphous with Parthéite.

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Crystals commonly prismatic, tabular, to 5 cm; also granular, massive.

Twinning:

Common on [101], may be lamellar.

Physical Properties

Cleavage:

[100] Perfect, [010] Perfect, [101] Imperfect

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Hardness (Mohs):

7.5

Density:

3.05 - 3.12 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Colorless, White, Grayish Blue, pale Blue, Pinkish

Transparency:

Transparent, Translucent

Luster:

Vitreous, Greasy

Refractive Index:

1.663 - 1.686  Biaxial ( + )

Birefringence:

0.0190 - 0.0210

Dispersion:

Strong to Very Strong

Pleochroism:

Weak; X = blue, pale brownish yellow; Y = deep bluish green, yellowish green; Z = colorless, yellowish

Occurances

Geological Setting:

Formed at high pressures and low temperatures, especially in low-grade regionally metamorphosed glaucophane schists; formed from plagioclase during saussuritization of gabbros and diabases; rarely in eclogites.

Common Associations:

Calcite, Crossite, Epidote, Garnet, Glaucophane, Jadeite, Muscovite, Pumpellyite, Quartz

Type Locality:

Reed Station, Tiburon Peninsula, Marin County, California, USA

Year Discovered:

1895

View mineral photos:

Lawsonite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Lawsonite is a very rare silicate mineral that is only found in a few locations worldwide. Gems are extremely rare and can be attractive with colorless, pale blue or pinkish colors and strong dispersion.

The main location for gem quality crystals is the type locality at Reed Station, Tiburon Peninsula, Marin County, California, USA. Other locations include Panoche Pass, San Benito County; in the Pacheco Pass area, Santa Clara County, California, USA; Darrington, Snohomish County, Washington, USA; the French and Italian Alps; and near Tavsanh, Turkey.
 

  
Lawsonite gems for sale:

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