Labradorite is a type of plagioclase, which is a homomorphic series composed of sodium feldspar (NaAlSi3O8, symbol Ab) and calcium feldspar (CaAl2Si2O8, symbol An). The composition of plagioclase is usually represented by the percentage of An molecules. Labradorite belongs to neutral plagioclase, with an An content of 50-70%. Pure and beautiful colored plagioclase can be used as a gemstone, but it is not very precious.
brief introduction
In 1770, a type of stone that could reflect iridescence was discovered in the eastern Labrador Peninsula of Canada, and it was officially named elongated stone. Later, elongated stones were also discovered in Australia, Finland, Madagascar, India, Mexico, and the Adirondack Mountains in the United States.
Stretching stones are quite common and are used as decorative materials by people, some of which have iridescent hues and are also used as gemstones. Stretching stones are generally gray, brown to black in color, and can be used as gemstones with red, blue, and green hues. The crystals of feldspar can reach up to 2 meters in length and are found in rocks such as gabbro, norite, basalt, and granulite.
Stretching stone, also known as spectral stone, is named after its ability to emit a rainbow of light similar to that of the sun. Widely present in various intermediate, basic, and ultrabasic rocks. Only a very small number of them can be used as gemstones.
Basic Information
Stretching stone, also known as labradorite in English, is a type of plagioclase that is generally composed of 30% to 50% sodium feldspar and 50% to 70% calcium feldspar molecules. In addition, there may be a small amount of potassium feldspar molecules and trace amounts of barium (BaO less than 0.2%), strontium (SrO less than 0.2%), iron (FeO+Fe2O3), and other impurities mixed in. Triclinic crystal system. Crystals are often in the form of plates or columns. White – gray white or gray black, occasionally yellow, brown, red, and green. Glass luster, transparent or slightly transparent. Two axis normal crystal,+2v=85 ±. Refractive index ng=1.562-1.672, nm=1.558～1.567，np=1.555—1.563； The folding rate is 0.007-0.012. The relative density is 2.69-2.2. Hardness of 6-6.5. Two sets of cleavage with plagioclase type and no fluorescence reaction.
Stretching stone is an important rock forming mineral that is widely present in various intermediate, basic, and ultrabasic rocks. Only a very small number of them can be used as gemstones. Due to the presence of clustered twin crystals or fine interaction layers of sodium feldspar formed by solid solution detachment, as well as occasional micro pores parallel to {010} crystal planes, the transparent or semi transparent varieties of elongated stones may exhibit some special optical effects. Some have milky luster and can be ground into plagioclase moonstone; Some have halo colors, called iridescent plagioclase.
