{"title":"Staurolite","description":"\u003cp\u003e\u003cstrong\u003eStaurolite\u003c\/strong\u003e is an iron-magnesium aluminum silicate, a classic nesosilicate index mineral of medium- to high-grade regional metamorphism, typically found in mica schists and gneisses alongside \u003cstrong\u003ealmandine garnet\u003c\/strong\u003e, \u003cstrong\u003ekyanite\u003c\/strong\u003e, \u003cstrong\u003emuscovite\u003c\/strong\u003e, \u003cstrong\u003ebiotite\u003c\/strong\u003e, \u003cstrong\u003esillimanite\u003c\/strong\u003e and \u003cstrong\u003echloritoid\u003c\/strong\u003e. Its name, from the Greek \"stauros\" for cross, reflects its most famous feature: cruciform penetration twinning, in which two prismatic crystals intersect at 60° to form a St. Andrew's cross or, more rarely, at 90° to form a perfect Greek cross. Crystals are typically reddish-brown to black, opaque, with a hardness of 7 to 7.5 on the Mohs scale, and are always found embedded in a host schist or gneiss matrix rather than lining open cavities. As a Barrovian index mineral, staurolite marks a precise window of temperature and pressure in prograde metamorphism, making it prized by petrologists as well as by mineral collectors. The world's finest twinned specimens come from the \u003cstrong\u003eKeivy Mountains\u003c\/strong\u003e on Russia's Kola Peninsula, where large, lustrous crosses sit on silvery muscovite schist matrix, including rare sixling intergrowths. \u003cstrong\u003ePizzo Forno\u003c\/strong\u003e in Ticino, Switzerland, is the classic Alpine locality, producing elongated crystals with associated kyanite, while the broader \u003cstrong\u003eLepontine Alps\u003c\/strong\u003e and \u003cstrong\u003eSaint Gotthard Pass\u003c\/strong\u003e region have supplied staurolite \"fairy crosses\" for centuries. Brittany, France, particularly the alluvial deposits at \u003cstrong\u003eBaud\u003c\/strong\u003e, \u003cstrong\u003eFinistère\u003c\/strong\u003e and near \u003cstrong\u003eScaër\u003c\/strong\u003e, has yielded floater crystals long collected as \"Pierre de Croix\" talismans, a tradition also echoed at \u003cstrong\u003eFanzeres\u003c\/strong\u003e in Portugal. In the United States, \u003cstrong\u003eFairy Stone State Park\u003c\/strong\u003e in Patrick County, Virginia, and \u003cstrong\u003eFannin County\u003c\/strong\u003e, Georgia — where staurolite is the official state mineral — are historic sources of cross-shaped twins, alongside New Hampshire's \u003cstrong\u003ePond Hill\u003c\/strong\u003e, Maine's \u003cstrong\u003eWindham\u003c\/strong\u003e locality, and the rare sixling twins of \u003cstrong\u003eHondo Canyon\u003c\/strong\u003e, New Mexico. Additional notable occurrences include Selbu in Norway, Nový Malín in the Czech Republic, Minnesota's Blanchard Dam, and Minas Gerais in Brazil. Collectors seek staurolite above all for its geometric cruciform twins, which combine scientific interest in crystallography with a long folk history as religious amulets and \"good luck\" charms. Well-formed, doubly terminated crosses on contrasting light-colored schist matrix, free of the pitting or artificial polish sometimes seen in tourist-trade fakes, command the greatest interest. Genuine specimens showing the mineral's characteristic \"Swiss cheese\" poikilitic texture with enclosed quartz, or paired with vivid blue kyanite and deep red garnet, make staurolite a rewarding centerpiece for any systematic or aesthetic mineral collection.\u003c\/p\u003e","products":[],"url":"https:\/\/www.italmineral.com\/collections\/staurolite.oembed","provider":"ITALMINERAL","version":"1.0","type":"link"}