Anorthite

specimen number:
1052815

location:
Nain Complex, Labrador, Newfoundland and Labrador, Canada

description:
A solid piece of anorthite, this is the variety known as labradorite, cut and polished on one face. Neat antique example that comes with the previous label as shown at the end of the video, this dates to the very early 20th century.

The coastal region of Labrador, Canada, particularly around Nain and Paul's Island, is a major geological locality noted for its massive quarrying of iridescent plagioclase feldspar. Geologically, the area is dominated by the Nain Anorthosite Complex, a vast Mesoproterozoic plutonic intrusion composed almost entirely of calcic plagioclase feldspar that cooled slowly deep within the crust, allowing for the growth of massive crystalline blocks. Small-scale surface extraction and collection began in 1770 when Moravian missionaries first noted the reflective rocks along the shoreline and began collecting specimens for European markets. Organized quarrying operations expanded intermittently through the nineteenth and twentieth centuries to supply decorative facing stone and mineral specimens, with modern industrial quarrying at sites like Tabor Island kicking off in the 1960s and continuing to export structural and ornamental stone into the twenty-first century.

Labradorite is a specific intermediate-to-calcic member of the plagioclase feldspar mineral series, traditionally associated as a rich variety of anorthite within the plagioclase framework. Geologically, it is defined by a chemical composition ranging between fifty and seventy percent of the pure calcium anorthite endmember, forming primarily in mafic igneous rocks like basalt, gabbro, and especially anorthosite. The mineral is characterized by its optical phenomenon known as labradorescence, which displays intense flashes of blue, green, gold, and copper colors. This iridescence does not come from surface features, but rather from the internal interference of light scattering off sub-microscopic exsolution lamellae, which are alternating layers of different feldspar compositions that separated during the slow cooling of the host magma.

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