Microcline

specimen number:
2292235

location:
Lake George, Colorado, USA

description:

A blocky prismatic terminated crystal of bluish green microcline, this a variety often called amazonite. In good condition all around.

The Lake George area, situated within Park County, Colorado, is a world-famous mineral locality celebrated for producing spectacular combinations of sharp amazonite crystals paired with lustrous smoky quartz. Geologically, the deposits are hosted within the Paleoproterozoic-age Pikes Peak granite batholith, a massive igneous intrusion characterized by highly evolved, coarse-grained granitic pegmatites. During the final stages of cooling, volatile-rich hydrothermal fluids accumulated in pressurized pockets called miarolitic cavities, providing the space and chemical conditions necessary for large, sharp silicate crystals to grow unimpeded. Artisanal surface prospecting and small-scale private claim mining began in the late 1800s, with systematic extraction intensifying in the mid-twentieth century as mechanized equipment became available. Private specimen mining and localized digging on active claims have remained continuously productive, with significant new pocket discoveries by independent mineral collectors extending well into the 2020s.

Amazonite is a distinct green to blue-green variety of microcline feldspar, a potassium aluminum silicate mineral that crystallizes in the triclinic system. The striking turquoise color is primarily caused by trace amounts of lead substituting for potassium ions within the crystal lattice, coupled with structural defects induced by natural, low-level background radiation over geological time. It typically occurs as well-formed prismatic crystals, often displaying characteristic Carlsbad or Baveno twinning habits that add structural complexity to the specimens. While found in several pegmatite fields worldwide, the sharp, blocky, intensely colored amazonite groups from the Lake George area, particularly when naturally intergrown with contrasting crystals of smoky quartz, represent the definitive standard for collectors.

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