Enstatite with Ilmenite

specimen number:
2282079

location:
Summit Rock, Klamath Co., Oregon, USA

description:
Iron rich crystals of enstatite across matrix with crystallized ilmenite.

Summit Rock, located in Klamath County, Oregon, is a prominent volcanic feature that has been utilized intermittently as a stone quarry, primarily for road metal and aggregate material used in local infrastructure. Geologically, the locality represents a late Pliocene to Pleistocene-aged andesite plug dome. The interior of this dense, fine-grained porphyritic rock contains numerous spherical vesicles and flat, lenticular cavities that formed as a result of late-stage volcanic gas exsolution and subsequent tearing within the cooling, semisolid magma. These open cavities feature linings of high-temperature, vapor-phase minerals, showcasing well-developed crystals of orthopyroxene (enstatite), plagioclase, augite, tridymite, magnetite, and hematite. Quarrying and mineral specimen recovery at the site became notably active during the mid-twentieth century, with comprehensive geological profiling of the cavity mineral assemblages published in 1970. Industrial rock extraction at the site has historically been conducted on an episodic basis by county and state road departments, with activity continuing into the late twentieth century.

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