Orthoclase with Albite

specimen number:
2072343

location:
Organ Mts., Dona Ana Co., New Mexico, USA

description:
Crystals of orthoclase, many showing twinning, measuring to 3.5 cm in height coming off matrix with white blocky crystals of albite. In good condition.

The Organ Mountains, located in Dona Ana County near Las Cruces, New Mexico, represent a spectacular tilted fault-block range primarily composed of the Organ Mountain Batholith. Geologically, this complex igneous feature consists of various phases of quartz monzonite, granite, and syenite that were emplaced during the Oligocene Epoch, approximately 27 to 33 million years ago. The district is recognized for its large, well-formed orthoclase crystals, which occur within pegmatitic pockets and miarolytic cavities; these crystals often exhibit classic Carlsbad twinning and can reach significant sizes, frequently characterized by their sharp, blocky habit. Historically, mining and quarrying in the Organ Mountains began in the late 19th century following the discovery of silver and lead deposits in 1849, with the most intense period of industrial operation occurring between the 1880s and the early 1930s. Notable sites like the Stephenson-Bennett Mine were major producers of base and precious metals during this era. While commercial metal mining has largely ceased, the area remains a significant locality for mineralogists and was designated as part of a National Monument in 2014 to preserve its unique geological and cultural heritage. As of 2026, the rugged peaks continue to be a source of study for their diverse igneous mineralogy and iconic orthoclase specimens.

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