Tourmaline, also known as tourmaline, has a molecular formula of (Na, Ca)(Mg, Fe)3B3Al6Si6(O, OH, F).
Hardness 6.96-7.85
Density 2.95-3.55 (usually 3.05)
Refractive index 1.60- 1.65
Birefringence: 0.0 18~0.040, generally 0.020.
Triangular system
Cleavage: no cleavage
Fracture: serrated or conchoidal fracture (related to crystallization habit)
Heterogeneous body
vitreous luster
Color: All colors appear in the spectrum.
Special optical effect cat's eye starlight discoloration
Occurrence and origin: columnar (more single crystals). Radial and fascicular (aggregate mineral specimens) occur in granite pegmatite and are found all over the world. Almost all of them are common in Brazil, Africa, Afghanistan and Asia, mainly Myanmar and Sri Lanka. In addition, China, Yunnan and California are the main producing areas of specimens!
The above are the main identification features of natural tourmaline, which can be seen everywhere. Now let's talk about the optimization of tourmaline, which is also the biggest headache for tourmaline now!
A kind of common red, green and blue beads dyeing, which generally dyes light color deeply, or dyes colorless with color. In the past, red was common, but now green and blue appear. Pay attention to the dye enrichment in the cracks, and the naked eye and ten times magnifying glass are enough!
Second, diffusion therapy, which should be the latest way. Tourmaline, which first appeared in Africa, usually appears in blue tourmaline. Light-colored surfaces diffuse into dark colors. Note that tourmaline will crack when heated unevenly, and the edge color can be seen in water darker than the middle (you can see by observation. This is usually detected in heavy liquid, but I found it obvious in water.
Three-film coating treatment, aluminum oxide coating on the surface, you can see the halo effect floating on the surface, which is easy to detect, but now the other film coating is blue, relatively shallow, and the overall color is similar to aquamarine, which is easy to see. Note that halo can basically be found by coating.
Fourthly, the heat treatment is basically from dark color to light color, which is not specified in the national standard, but we can see that almost 40% of the original gas-liquid inclusions have radial whiskers on their edges under a magnifying glass, and the color transition of multi-color and two-color tourmaline will have a wavy effect, which looks like myopia! Legend has it that Europe can turn green tourmaline into pale blue green tourmaline (Pallai Pase).
5. Irradiation treatment is common in tourmaline produced in Afghanistan. It should be noted that light green and light blue green (Paleba color) can also be used to process pink into deep red. This test is a bit difficult, so I gave up with the naked eye and needed instrument testing.