Faldshpathoids (silicates): Analcim
Diagnostic card.
On the picture. Pinkish crystals of analcime.
Na Al Si 2 O 6 * H 2 O
Cubic amount of cubic zirconia
Hardness 5,5
Specific weight 2.24-2.29
Cleavage unclear
Cracked shell
Color is colorless, differently colored
Color in powder white
Glitter glass
Crystals of this very common mineral sometimes are the size of a fist. There are both colorless and transparent, and opaque, painted in white or reddish white. If they have their own characteristic features, then it is almost impossible to confuse them with another mineral. The crystal has quadrangular trapezoidal faces, so it is called the trapezohedron, or tetragon-trioctahedron. Analcim has medium hardness, glass shine, unclear cleavage. It is recognized by these features, according to the shape of the crystals and by its fusibility.
Chemical composition. Sodium oxide (Na2O) 14.07%, alumina (Al2Os) 23.29%, silica (SiO2) 54.47%, water (H2O) 8.17%. The shape of the crystals. Tetragon-trioctahedra (leucithohedra). Class of symmetry. Hexaoctahedral - m3m. Aggregates. Solid, granular, dense, earthy.
Analcim. Transparent crystals (up to 1.5-2 cm) in the voids of the rock.
Cyclopean Islands, near Catania, Sicily, Italy. Photo: © А.А. Evseev.
Analcim. Large crystal ~ 9 cm. Alpe di Susie, Ju. Tirol, Italy.
At the bottom. Analcim. Crystals up to 5 cm. Val di Fassa, Ju. Tirol, Italy. Photo: © А.А. Evseev.
Diagnostic signs.
When heated in a glass tube, it becomes turbid and emits water vapor settling on its cold walls. Easily fuses. Behavior in acids. It decomposes in HCl. Colorless, gray, white with a yellowish tinge, meat-red.
Origin.
Analcim is common in various geological settings (magmatic, sedimentary, metamorphic). Occasionally it is found in the form of magnificent crystals in voids of igneous rocks, such as basalts and andesites.
Place of Birth.
In Italy, analcime is found in many places. In the Montevecchio-Major (in the province of Vicenza) basins, it is easy to find small shiny, clear and colorless crystals. Larger crystals, opaque and reddish-white, are known in the Alpe di Susi (Bolzano province), Val di Fassa (Trento province) and Vicentino. In Sicily, fine crystals of analcime were found on the island of Cyclops, a rocky formation opposite Aci-Trezza. Particularly beautiful transparent crystals exist on the islands near Catania (Sicily) and the Gulf of Naples (Italy); In the mountains of Bohemia (Czech Republic) and near Braunschweig (Germany)
Analcim. Lake deposit, Av. Siberia, Russia. Photo: © А.А. Evseev.
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