Mineral Information and Data:

CaAl2Si2O7(OH)2 • H2O [CNMNC approved formula]

Named for Andrew Cowper Lawson (1861-1952), Scottish-American geologist, University of California, Berkeley, California, USA.

IMA status : Valid species (Pre-IMA 1895) Grandfathered
(8th edition) :  
  (56) Sorosilicate Si2O7 Groups and O, OH, F. and H2O
  (56.02) with cations in [4] and/or >[4] coordination
  (56.02.03) Lawsonite - Ilvaite group
(10th edition) :
  (09) Silicates
  (09.B) Sorosilicates (dimer) structures
  (09.BE) Si2O7 groups, with additional anions; cations in octahedral [6] and greater coordination
Crystal system: Orthorhombic System
Point group (H-M): mmm (or 2/m 2/m 2/m) — dipyramidal
Unit cell: a = 8.795(3) Å, b = 5.847(1) Å, c = 13.142(6) Å, Z=4
Crystal Habit: Crystals commonly prismatic, tabular, to 5 cm; also granular, massive.
Twinning: Common on {101}, may be lamellar.
Color: Colorless, white, pale blue to grayish blue; colorless to bluish green in thin section
Diaphaneity: Translucent
Luster: Vitreous, greasy
Hardness (Mohs): 6
Measured Density: 3.05 - 3.12 g/cm3
Cleavage: Perfect on {100} and {010}, imperfect on {101}
Tenacity: Brittle
Streak: White
Polymorphism and Series: Dimorphous with partheite.
Geologic 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
Mineral Association: Pumpellyite, epidote, garnet, crossite, muscovite, jadeite, glaucophane, quartz, calcite.
Other Properties: Gemstone Unlikely Available.


Glaucophane schist with a heavy druse of lawsonite crystals to 0.7 cm
Origin: Reed Station, Tiburon, Marin Co., California, USA
Sample size: 7.2 x 6 cm
Photo: John Veevaert, Trinity Mineral Co.


(zoom-in of above)


White to light blue square, tabular crystals to 1.5 cm in glaucophane schist.
Origin: Tiburon Peninsula, Marin Co., California, United States (type locality)
Sample size: 8.5 x 6 x 3.5 cm
Photo: Tom Loomis


(zoom-in of above)