Gyrolite - Encyclopedia

    Class : Silicates
    Subclass : Phyllosilicates
    Crystal system : Triclinic
    Chemistry : NaCa16(Si23Al)O60(OH)8 14H2O
    Rarity : Rare to uncommon

Gyrolite is a phyllosilicate from the cavities of basaltic lavas, which are usually accompanied by zeolites. Its name comes from the Greek guros (circle, round), recalling the ball arrangement of its crystals. It appears in flattened pseudohexagonal micaceous lamellae frequently grouped in rosettes and fans, or in globular clusters composed of lamellar crystals in a radial arrangement. Gyrolite is white to pale greenish, sometimes grayish, yellow-green or brownish.

Main photo : Gyrolite from Bombay, India

Gyrolite from Malad Quarry, Maharashtra, India © Rock Currier
Gyrolite from Ljósá Quarry, Faroe Islands © Volker Betz
Gyrolite from Monument quarry, Oregon, USA © Rudy W. Tschernich
Gyrolite from Malad Quarry, Maharashtra, India © Gianfranco Ciccolini

Gyrolite in the World

The spherical aggregates exceeding 5 cm in diameter associated with okenite and apophyllite constitute remarkable specimens extracted from the basalt quarries of Mumbai (Khandivali), Nasik or Poona (India). 1 cm spherules occupying basaltic and doleritic cavities are known in Scotland (notably on the Isle of Skye), where this mineral was discovered, and further north in the basalts of the Faroe Islands, in well-formed centimeter-sized crystals. Gyrolite is also reported in California (Crestmore, New Almaden) and in Canada in the Bay of Fundy (Nova Scotia).

Gyrolite in France

In France, gyrolite is reported at Puech de Vermus near Espalion (Aveyron), in the basalt quarry of Châteaugay (Puy-de-Dôme) in centimeter-sized yellow balls, in the Tuamotu archipelago in French Polynesia and in Reunion.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 2.5
Density : 2.45 to 2.51
Fracture : Irregular
Streak : White

TP : Translucent to transparent
RI : 1.535 to 1.549
Birefringence : 0.014
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None

Solubility : -

Magnetism : NoneRadioactivity : None

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