Cassiterite after Orthoclase

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Classic Cornish pseudomorph specimen from 1828. This is a cluster of twinned orthoclase crystals, now replaced by cassiterite. In super condition all around. The specimen comes with a previous antique label as shown at the end of the video. A wonderful thumbnail specimen.Wheal Coates, perched on the dramatic cliffs of St Agnes in Cornwall, England, is a world-renowned mineralogical locality famous for its remarkable pseudomorphs of cassiterite after orthoclase. Geologically, the mine is situated within the contact zone of the St Agnes granite and surrounding Devonian metasedimentary rocks, known locally as killas. Hydrothermal activity in this region led to the replacement of large, carlsbad-twinned orthoclase feldspar crystals by fine-grained cassiterite (tin oxide), resulting in specimens that preserve the distinct monoclinic form of the original feldspar but possess the heavy, dark properties of tin ore. Historically, mining and quarrying at the site date back to at least the 17th century, with the most significant period of activity occurring during the mid-19th century under various leases between 1802 and 1889. The most famous "pseudomorph pocket" was discovered in 1828, yielding the iconic specimens that now reside in major museum collections globally. While the mine saw a brief period of reconstruction and limited production between 1911 and 1914, it proved uneconomic and was abandoned shortly thereafter.Themak Ede (active late 19th and early 20th century) was a Hungarian mineral dealer based in Temesvar, which was then part of the Austro-Hungarian Empire and is now Timisoara, Romania. He operated during a golden age of European mineralogy, specializing in high-quality specimens from the prolific mining districts of the Carpathian Mountains and the Banat region. Themak is particularly noted for his contributions to mineralogical science through the distribution of rare and well-crystallized species from localities such as Dognacska (Dognacecea) and Vasko (Ocna de Fier).