Lazurite's rating and difference

2021-08-13

The quality evaluation of lapis lazuli can be based on color, clarity, weight (lumpness) and other aspects.
colour
The color of lapis lazuli is determined by the content of the lapis lazuli mineral. If it contains more lapis lazuli minerals, the color is good, otherwise the color is worse. Because the lapis lazuli mineral is blue, the lapis lazuli jade is general It is also blue, and the best blue tone is strong, pure and uniform. If the color is intertwined with white stone lines or white spots, it will reduce the density, purity and uniformity of the color, and thus the quality will be reduced.
Cleaness
Clarity is an important factor in evaluating the quality of lapis lazuli. The texture is dense, tough, and delicate, with a lot of lapis lazuli minerals and less other impurity minerals (such as calcite, pyroxene, mica, blue ashlar, etc., but may contain a small amount of pyrite evenly distributed in star-like patterns). Jinshi is top grade. If the pyrite is distributed locally in pieces, it will affect the texture of lapis lazuli, which in turn will also affect the quality of lapis lazuli. For lapis lazuli containing impurity minerals, the uniformity of the impurity mineral distribution will also be a criterion for evaluating its texture. It is generally believed that the uniform distribution of impurity minerals has a higher quality level than the uneven distribution, and vice versa, the lower the quality level.
Weight (Lumpness)
It refers to the size of the lapis lazuli block. Under the same quality conditions, the larger the volume of the lapis lazuli, the higher its value.
According to the above evaluation criteria, lapis lazuli can be divided into the following grades in order, and the grades are successively lowered:
(1) Lapis Lazuli: The highest quality lapis lazuli. The lapis lazuli mineral content is more than 99%, does not contain pyrite, and there are few other impurity minerals. The texture is dense, tough, and delicate, showing a strong, pure and uniform blue.
(2) Lapis lazuli grade: the mineral content of lapis lazuli is generally 90-95%, without white spots, and may contain sparse star-shaped pyrite and a small amount of other impurity minerals, the texture is relatively pure, dense, and delicate, and the color concentration and uniformity , The purity is worse than the lapis lazuli level.
(3) Jinkelang grade (Jingelang grade): The content of lapis lazuli minerals is significantly reduced, and it contains more and dense pyrite, and the content of impurity minerals is significantly increased, with white spots and white flowers, and the color concentration is significantly reduced. It is light blue and unevenly distributed.
(4) Accelerating stone grade: This type of lapis lazuli is the worst quality lapis lazuli jade. It contains the least lapis lazuli minerals and generally does not contain pyrite. The content of impurity minerals such as calcite increases significantly, and only star-shaped blue is seen on the jade. Color distribution, or mixed with blue and white spots.

The difference between lapis lazuli and similar jade. Sodalite, blue ashlar and azurite are easily confused with lapis lazuli. The fakes and substitutes of lapis lazuli include colored jasper, colored spinel, colored Xiuyu, imitation lapis lazuli, and dyed marble. The characteristics of similar jade are as follows:
Sodalite is semi-transparent, coarse-crystalline structure, uniform in color, with initial cleavage and white calcite minerals visible. The hardness is 5.5-6, the density is 2.25, the refractive index is 1.483, and the color filter is brownish red [2].
Blue ashlar, orange-red fluorescence, density 2.44-2.5g/cm3, refractive index 1.49-1.504.
Azurite has a small hardness of 3.5-4, a refractive index of 1.73-1.83, and is brittle without large compact blocks.
Colored jasper (also known as Swiss green gold) is artificially colored with chalcedony and other fake materials. It has a high hardness of 6.5-7 and a refractive index of 1.54-1.55.
Colored spinel (also known as colored cyan), artificially colored with cobalt salt, granular structure, strong luster, uniform color, refractive index 1.72-1.73, visible cobalt absorption spectrum under the spectroscope, showing under the Charles filter Bright red.
Colored Xiuyu (also known as blue gold), light blue, no pyrite, strong grease luster, hardness 2.5-6, refractive index 1.56-1.57.
Imitation green gold, can be imitated with glass, made of colored dark blue sulfur or glass, no pyrite can be seen, glass luster, shell-like fracture, brittle.

Dyed marble, with low hardness, is easy to move with a knife, and has a granular structure. It reacts obviously when it encounters hydrochloric acid.