Leucite
Leucite is a mineral this is certainly rock-forming of aluminium and potassium tectosilicate K[AlSi2O6]. Crystals have the type of cubic icositetrahedra but, as first observed by Sir David Brewster in 1821, they may be not optically isotropic, and are also therefore pseudo-cubic. Goniometric measurements created by Gerhard vom Rath in 1873 led him to mention the crystals to the operational system this is certainly tetragonal. Optical investigations have since proved the crystals to be still more complex in character, also to consist of several orthorhombic or monoclinic individuals, which can be optically biaxial and repeatedly twinned, giving rise to twin-lamellae and also to striations from the faces. After the crystals are raised to a temperature of approximately 500 °C they become optically isotropic in addition to twin-lamellae and striations disappear, as they reappear in the event that crystals are cooled again. This character this is certainly pseudo-cubic of is a lot like when compared to mineral boracite.
Leucite is really a known member of the Feldspathoid Group of minerals that includes Cancrinite, Haüyne, Lazurite, Leucite, Nepheline, and Sodalite. Minerals with chemistries being near to those of the feldspars that are alkali but are bad in silica (SiO2) content are known as Feldspathoids. Leucite is numerous in various lava rocks but is extremely uncommon in facetable crystals. Gems usually are cloudy and tiny or included. The source that is mainly of Leucite crystals adequate for faceting is the Alban Hills, near Rome, Italy.
The are numerous localities worldwide. Especially from Italy, as at Vesuvius, Monte Somma, and Roccamonfina, Campania; at Villa Senni, Frascati, and Ariccia, Lazio; and on Vulcano, Lipari Islands. Across the Laacher See, Eifel district, Germany. In the united states, from the Leucite Hills, Sweetwater County, Wyoming; the Bear Paw Mountains, Hill County, Montana; and at Magnet Cove, Hot Spring County, Arkansas. Within the West Kimberley region, Western Australia. In Tanzania, on Kilimanjaro. In Uganda, discovered around Ruwenzori and Kariya. From Mt. Nyiragongo, Kivu Province, Congo (Zaire).
| Category: | tectosilicates |
| Chemical Formula: | KAlSi2O6 |
| Potassium Aluminum Silicate | |
| Molecular Weight: | 218.25 gm |
| Composition: | Potassium | 17.91 % | K | 21.58 % | K2O |
| Aluminum | 12.36 % | Al | 23.36 % | Al2O3 | |
| Silicon | 25.74 % | Si | 55.06 % | SiO2 | |
| Oxygen | 43.99 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Cleavage: | Indistinct; very poor on {110} |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 5.5 – 6.0 |
| Density: | 2.45 – 2.50 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Barely Detectable; GRapi = 255.81 (Gamma Ray American Petroleum Institute Units) |
| Crystallography: | Tetragonal – Dipyramidal |
| Crystal Habit: | Commonly euhedral, pseudocubic crystals, to 9 cm, typically showing fine twin striae. As disseminated grains; rarely granular, massive. |
| Twinning: | Common and repeated on [110], [101], and other orientations, from two complex displacive phase transformations during cooling. |
| Color: | White, gray; colorless in thin section. Yellowish and reddish tints possible due to impurities. |
| Transparency: | Transparent to Translucent, Opaque |
| Luster: | Vitreous |
| Refractive Index: | 1.508 – 1.509 Uniaxial ( + ); may be anomalously Biaxial |
| Birefringence: | 0.001 |
| Dispersion: | Moderate |
| Pleochroism: | None |
