Lawsonite - Encyclopedia

    Class : Silicates
    Subclass : Sorosilicates
    Crystal system : Orthorhombic
    Chemistry : CaAl2Si2O7(OH)2 H2O
    Rarity : Common

Lawsonite is a calcium silicate typical of high pressure and low temperature metamorphic rocks (blue schists). It is also a mineral that forms by alteration of plagioclase feldspars. It is a common companion of epidote, garnet (almandine), pumpellyite and glaucophane. It was named in honor of Andrez Cowper Lawson, Professor of Geology at the University of California. It is a mineral which occurs in prismatic to tabular crystals, not exceeding 5 cm. Lawsonite is colorless, gray to bluish or grayish pink, exceptionally emerald green when chromiferous.

Main photo : Lawsonite from Mendocino County, California, USA © Eugene & Sharon Cisneros

Lawsonite from Valley Ford, Sonoma County, California, USA © Rock Currier
Chromian lawsonite from Cape Marmari, Syros island, Greece © Jyrki Autio
Lawsonite from Mendocino County, California, USA © Mike Keim
Lawsonite from the island of Groix, Morbihan, France © Michel Arliguie

Lawsonite in the World

The largest known lawsonite crystals come from California and more precisely from the Tiburon Peninsula and Covelo where they can reach 5 cm. Good specimens also exist in several Japanese and Welsh localities. Superb intense green centimeter-sized crystals were discovered in 2012 in Cape Marmari (Greece).

Lawsonite in France

In France, lawsonite is known in centimetric crystals with a diamond section in the glaucophane schists of the island of Groix (Morbihan), they are completely transformed into various phyllosilicates.

Twinning

No twins known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 7.5
Density : 3.1
Fracture : Irregular
Streak : White

TP : Translucent to transparent
RI : 1.665 to 1.685
Birefringence : 0.020
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Insoluble

Magnetism : NoneRadioactivity : None

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