Calcite with Quartz (G-021)

specimen number:
9273050

location:
Asuncion mine, Guanajuato, Mexico

description:
A plate of crystallized purple quartz, the variety known as amethyst, partially coated with crystallized colorless calcite. This is in good condition.

The Guanajuato mining district, situated in the central highlands of the State of Guanajuato, Mexico, is a legendary underground mining center world-renowned for its immense historical silver-gold production and for providing fine mineral specimens of amethyst, acanthite, pyrargyrite, and calcite. Geologically, this major district is a classic low-to-intermediate sulfidation epithermal vein system localized within a thick sequence of Mesozoic volcanic and sedimentary rocks that were heavily disrupted by mid-Tertiary tectonic extension. Mineralization occurred during the Oligocene epoch along three primary fault systems, most notably the Veta Madre (Mother Lode), where boiling hydrothermal fluids ascended through faults to deposit rich silver sulfides and electrum within a structural gangue of quartz, adularia, and calcite. Historically, silver was discovered by Spanish prospectors in 1548, leading to the establishment of legendary mines like La Valenciana, which by the late eighteenth century produced a significant percentage of the entire world's silver output. Mining operations continued through the turbulent years of the Mexican War of Independence, followed by revitalization under British, American, and local cooperative ownership throughout the nineteenth and twentieth centuries. Through 2026, while the historic cooperative era has shifted toward consolidation under major multinational mining corporations, active underground extraction and exploration continue to yield metals and collector specimens, solidifying Guanajuato as a foundational global geological benchmark for studying epithermal vein architecture and silver mineralization.

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