Azurite with Malachite

specimen number:
2102379

location:
Blue Grotto prospect, San Juan Co., Utah, USA

description:
Sparkling blue crystallized azurite across both sides of matrix with minor malachite some damage present as seen.

The Blue Grotto prospect, situated at the head of Big Indian Valley within the Lisbon Valley Mining District of San Juan County, Utah, United States, is a classic American mineral locality celebrated for producing exceptional, highly lustrous azurite crystal clusters and spherical nodules. Geologically, this deposit is located on the downthrown side of the Lisbon Valley Fault along the flank of a major salt-core anticline, where copper mineralization is hosted within the porous sandstones and conglomerates of the Late Cretaceous-age Dakota Formation. During younger post-depositional events, deeply circulating, oxidized basinal brines migrated upward along the fault network, leaching copper from underlying red beds and reprecipitating rich secondary copper carbonates, including malachite and vibrant blue azurite rosettes, inside a prominent, 100-foot-wide kaolinite-filled clay vein and localized solution fractures. Historically, the prospect originated as part of the broader Big Indian copper mining property, where localized open-cast quarrying, surface stripping, and exploratory tunneling for industrial copper ore occurred sporadically following the initial organization of the district in 1892 and a surge in mining activity around 1903. While primary commercial ore operations for industrial metals slumped mid-century, specialized specimen quarrying exploded at the Blue Grotto site following the discovery of world-class azurite pockets by field collectors in 1978, leading to a prolific era of specimen extraction throughout the 1980s.

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