Byssolite - Encyclopedia

    Class : Silicates
    Subclass : Inosilicates
    Crystal system : Monoclinic
    Chemistry : Ca2(Mg,Fe)5Si8O22(OH)2
    Rarity : Fairly common

Byssolite is an asbestiform variety of actinolite, common in alpine deposits, especially alpine clefts. Its name comes from the Greek bussos (cloth) and lithos (stone), alluding to the fibrous appearance of its crystals. Usually pale greenish-grey in color, byssolite forms very fine mats or aggregates. It is frequently associated with chlorite, epidote and talc, as well as many other minerals resulting from metamorphism. It is part of "asbestos" and has been used for the manufacture of fire retardants.

Byssolite in the World

Byssolite is a fairly widespread variety. Magnificent decimetric felts composed of extremely fine millimetric crystals have been discovered at New Melones Lake (Calaveras County, California). Very fine specimens have also been extracted from Monte Redondo dolerite in Portugal.

Byssolite in France

The French Alpine clefts have provided spectacular samples, notably those of the Combe de la Selle (Isère) where the byssolite is associated with superb helmets of green prehnite.


Simple and parallel twins on {100}; lamellar and parallel to {001} but not visible to the naked eye.

Fakes and treatments

No fake identified for this mineral species.

Hardness : 5 to 6
Density : 3.03 to 3.24
Fracture : Irregular
Streak : White

TP : Translucent to transparent
RI : 1.613 to 1.666
Birefringence : 0.023
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None

Solubility : Insoluble

Magnetism : Paramagnetic
Radioactivity : None


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