Montebrasite
specimen number:
2262334
location:
Midnight Owl Mine, Yavapai Co., Arizona, USA
description: The Midnight Owl mine, located along Independence Gulch within the White Picacho mining district of Yavapai County, Arizona, was a notable producer of lithium, beryllium, and industrial feldspar. Geologically, the deposit consists of several irregular, broadly tabular Proterozoic-age granitic pegmatite dikes that cross-cut ancient quartz-hornblende-mica gneiss and quartz-muscovite schist country rock. These pegmatites exhibit extreme internal zoning, featuring large structural bulges where incompatible elements became highly concentrated into very coarse-grained mineral phases, including massive pods of spodumene and what was historically classified as amblygonite, though modern analytical work has formally reclassified this lithium phosphate mineral as hydroxyl-dominant montebrasite. These phases are hosted alongside blocky perthite feldspar, quartz, mica, and scattered crystals of beryl and tantalum-niobium oxides. Historically, the outcropping pegmatite was recognized for its strategic mineral content in the mid-twentieth century, with active commercial extraction commencing in 1947. Operations primarily utilized open-cut quarrying methods, focusing on the thick western and eastern bulges of the main dike to supply high-purity beryl for aerospace applications and lithium ore for industrial manufacturing. Regular commercial production at the site continued through 1952, with smaller intermittent extractions and shipments of beryllium and lithium ores extending until 1963. Following this period, the property saw localized corporate exploration and bulk-sample testing programs for tantalum and lithium during the mid-1980s, and while commercial extraction remains inactive, the property continues to see modern exploration and geological mapping activities through 2026.
A white mass of montebrasite. At one time these were supposed to of been amblygonite, they have since been proven to be montebrasite. Good rich example for the locality.
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