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Geologic Occurrence of Labradorite
Labradorite is found in igneous, metamorphic, and sedimentary rocks. It most often occurs as a primary mineral in mafic igneous rocks such as basalt, gabbro, and norite. It is also found in anorthosite, an igneous rock in which labradorite can be the most abundant mineral. Labradorite occurs in gneiss that has been produced through the metamorphism of labradorite-bearing igneous rocks. It is also found…
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Cutting Labradorite
Labradorescent material is most often cut into cabochons. The labradorescence phenomenon is best exhibited when the base of the cabochon is parallel to the layers in the material that produce the labradorescent flash. Careful study of the material is required so that the finished stone will be oriented to produce a full “face-up color.” If…
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Labradorite as a Gemstone
Labradorite has become a popular gemstone because of the unique iridescent play-of-color that many specimens exhibit. The quality, hue, and brilliance of the labradorescence varies from one specimen to another and within a single specimen. Stones with exceptional color are often given the name “spectrolite.” Labradorite is rarely seen in mass-merchant jewelry. Instead it is most often…
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What Causes Labradorescence?
Labradorescence is not a display of colors reflected from the surface of a specimen. Instead, light enters the stone, strikes a twinning surface within the stone, and reflects from it. The color seen by the observer is the color of light reflected from that twinning surface. Different twinning surfaces within the stone reflect different colors…
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What Causes Labradorescence?
Labradorescence is not a display of colors reflected from the surface of a specimen. Instead, light enters the stone, strikes a twinning surface within the stone, and reflects from it. The color seen by the observer is the color of light reflected from that twinning surface. Different twinning surfaces within the stone reflect different colors…
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Labradorite
What is Labradorite? Labradorite is a feldspar mineral of the plagioclase series that is most often found in mafic igneous rocks such as basalt, gabbro, and norite. It is also found in anorthosite, an igneous rock in which labradorite can be the most abundant mineral. Some specimens of labradorite exhibit a schiller effect, which is a strong play of iridescent blue, green, red, orange,…
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13. Synthetic Spinel
Synthetic spinel was first produced in 1847, but little was used in jewelry until the early 1900s. By the 1930s, synthetic spinels in a wide variety of colors were being made by the Verneuil and flux growth processes. These colored spinels were given trade names such as “tourmaline green spinel” and “cobalt blue spinel”. Much…
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12. Black Spinel
Ceylonite and pleonaste are names used for black spinel. These names are also used for gray and blue spinels that are so dark that they appear to be black (unless they are examined with a bright light). Although these dark spinels are not commonly seen in jewelry, they are exceptionally durable because of their hardness.…
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11. Round and Cushion Cut Spinel
Spinel is frequently faceted into round and cushion cut (square with rounded corners) gems. These faceted shapes can be efficiently cut from octahedral spinel crystals with a minimal amount of lost weight.
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10. Beautiful Crystals
Like diamond, spinel often crystallizes in perfect octahedral crystals. An octahedron is a three-dimensional shape that resembles two four-sided pyramids attached at their bases. Octahedral crystals of spinel are often mined from marble, but they are more often found as water-worn crystals in stream sediments. Especially nice crystals are highly prized by mineral collectors or…