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What Are Geodes?
Geodes are spherical to subspherical rock structures with an internal cavity lined with mineral materials. They have a durable outer wall that is more resistant to weathering than the surrounding bedrock. This allows the geode to survive intact when the surrounding bedrock weathers away. The mineral lining the cavity is often a scintillating druse of tiny quartz crystals underlain by multiple…
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A “Gemmy” Architectural Stone
Some deposits of anorthosite are quarried and cut into slabs that are used to manufacture small sculptures, countertops, window sills, tiles, facing stone, and other architectural products.
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Notable Labradorite Localities
Labradorite is named after its location of discovery on the Isle of Paul, near Nain, Labrador, Canada. It was discovered there in 1770 by a Moravian missionary. Labradorite with superb labradorescence is produced from a few deposits in Finland. The best of this material was given the name “spectrolite” by the director of the Geological…
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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…