nephelines

Nephelines are a group of tectosilicate minerals within the feldspathoid group. They have the chemical formula (Na,K)AlSiO4. Nephelines are characterized by their glassy luster and typically form in silica-poor, alkali-rich igneous rocks. They are rarely found in coarse crystals, usually appearing as granular or massive aggregates. Commonly, nephelines are colorless to white, but they can also be gray, yellowish, or reddish due to impurities. The mineral is relatively soft, with a hardness of around 5.5 to 6 on the Mohs scale, and has a specific gravity of approximately 2.55 to 2.65. Nepheline exhibits conchoidal fracture. It is an important rock-forming mineral in undersaturated igneous rocks such as nepheline syenites, phonolites, and some trachytes. Nepheline can also occur in certain metamorphic rocks. Alteration of nepheline can lead to the formation of other minerals like kaolinite or mica. While not a primary ore mineral, nepheline has some industrial uses, particularly in the glass and ceramic industries due to its aluminum and alkali content. It is also sought after by mineral collectors. The name "nepheline" derives from the Greek word for "cloud," referring to its tendency to become cloudy when altered.