Andalusite

specimen number:
1052708

location:
Fresno Co., California, USA

description:
A set of five thick crystals of andalusite. This comes with an antique label as shown in the video and picture. Size provided is the size of the label. These were acquired through the dealer Lazard Cahn in 1913.

Chiastolite is a distinctive, globally recognized variety of the aluminum silicate mineral andalusite that is characterized by the presence of a prominent, dark carbonaceous cross or cruciform pattern running through its crystal core. Geologically, this unique mineral forms within argillaceous or clay-rich sedimentary rocks that underwent low-pressure, low-to-medium grade contact metamorphism, typically occurring in the thermal aureoles surrounding large, intrusive granitic plutons. As the andalusite crystals rapidly grow in the heat-altered shale or slate, graphite and other carbonaceous impurities from the host rock are systematically pushed aside, selectively accumulating along the rapid-growth crystalline junctions to form the symmetrical, dark gray-to-black internal geometric patterns. Historically, these natural cross stones have been collected for centuries across classic old-world localities like Santiago de Compostela in Galicia, Spain, as well as nineteenth-century American sites like Lancaster, Massachusetts, where they were traditionally cut and polished into circular cabochons or talismans for personal adornment.

Lazard Cahn (1865-1940) was a prominent American mineral dealer and self-taught crystallographer based in Colorado Springs who became one of the most respected figures in the field during the late 19th and early 20th centuries. He was widely recognized for his exceptional ability to identify rare species and for his meticulous study of crystal forms, eventually having the borate mineral cahnite named in his honor. Cahn operated a high-end mineral dealership that catered to major museums and elite private collectors, specializing in rare alpine minerals and classic American localities. His professional career was marked by significant contributions to mineralogical literature, including his work on the micromounting of specimens and his detailed descriptions of complex twinning laws.

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