Sanidine

specimen number:
2282044

location:
Taiji, Higashimuro-gun, Wakayama, Japan

description:
A grouping of colorless blocky sanidine crystals. In good condition.

The Taiji area, situated within the Higashimuro District of Wakayama Prefecture, Japan, is historically notable for its small-scale, localized mining and quarrying activities that targeted specific geological formations along the Kii Peninsula. Geologically, the region is dominated by complex sedimentary sequences belonging to the Shimanto Accretionary Prism and Miocene volcanic-plutonic complexes, including felsic igneous rocks and tuffaceous layers associated with the Kumano Acidic Rocks. Small-scale quarrying operations for local structural stone and minor prospecting for metallic mineral traces occurred intermittently during the late nineteenth and early twentieth centuries, particularly around the 1890s through the 1920s. While never developing into a major industrial mining hub, the geological exposures created by these historic cuts and coastal erosion have provided researchers with valuable insights into the tectonic and magmatic history of southwest Japan.

Sanidine is a high-temperature potassium feldspar mineral that crystallizes in the monoclinic system and is a dominant constituent of felsic volcanic rocks. Geologically, it forms in rapidly cooled volcanic extrusions like rhyolite, dacite, and trachyte, as well as in shallow intrusive rocks, where the fast cooling rate preserves a disordered crystal structure that stabilizes at extreme temperatures. The mineral typically occurs as colorless, white, or light gray tabular crystals or glassy phenocrysts that exhibit a vitreous luster, perfect cleavage, and often distinct Carlsbad twinning. Because it contains significant amounts of potassium and remains stable unless subjected to prolonged metamorphic reheating, sanidine is one of the most reliable and widely used minerals for potassium-argon dating of ancient volcanic eruptions.

Questions about this specimen?
Send an email or call us: 314-341-1811.