Analcime - Encyclopedia

    Class : Silicates
    Subclass : Tectosilicates
    Crystal System : Triclinique
    Chemistry : NaAlSi2O6 . H2O
    Rarity : Quite common

Analcime is a mineral whose composition, structure and origins are similar to zeolites and feldspathoids, a group in which it is sometimes classified. It is a low temperature hydrothermal mineral that occupies the cavities of volcanic rocks (basalts, trachy-basalts and more rarely phonolites). It is associated with zeolites and prehnite, but it can also be found in nepheline syenites and their pegmatites. It forms a series with pollucite. The analcime owes its name to the Greek analkis (weak) to emphasize the low electrostatic charge that this mineral develops when heated or rubbed. The crystals can be large (sometimes decimetric), usually trapezoidal, exceptionally cubic. They are colorless, more often milky white, sometimes pink, occasionally yellowish or greenish. It is a mineral that presents no particular use, crystallized specimens are sought after collectors.

Analcime in the World

The deposits of analcime are very numerous. The best specimens in the world are superb brilliant trapezohedra up to 25 cm, associated with large crystals of serandite, aegyrine and natrolite discovered at Mont Saint-Hilaire, Quebec. Beautiful pinkish-white trapezohedra exceeding 10 cm and well formed cubes come from several sites in Val di Fassa (Trentino, Italy). The localities of Nidym and Toura in central Siberia also give superb white crystals of 18 cm. The typical locality of the rocks of Cyclops, facing Catania (Sicily, Italy) is known for its beautiful centimetric clear crystals. Coleman (Alberta, Canada) produces stunning red crystals, and Kings Valley and Springfield (Oregon) produce stunning 6 cm clear crystals.

Analcime in France

In France, analcime is known in large weathered crystals at Port d'Agrès (Aveyron) and in the cavities of several Auvergne basalts (Puy de Marmant, Puy Griou). The beautiful gemmy microcrystals of analcime are present in the peperites of Pont-du-Château (Puy-de-Dôme).
Analcime from Port d'Agrès, Aveyron, France
Analcime from Port d'Agrès, Aveyron, France
Analcime from Port d'Agrès, Aveyron, France
Analcime from Port d'Agrès, Aveyron, France

Twinning

The analcime frequently shows polysynthetic twins on {001} and {110} visible only in thin section under polarized analyzed light.

Fakes and scams

No fake inventories for this species.



Hardness : 5 to 5.5
Density : 2.24 to 2.29
Fracture : Sub-conchoidal

Streak : White



TP : Translucent to transparent
IR : 1.479 to 1.494
Birefringence : 0.001
Optical character : Biaxial -
Pleochroism : Very weak to none
Fluorescence : 
Brown to white


Solubility : Hydrochloric acid

Magnetism : None
Radioactivity : None