How are the grades of crystals classified?

Crystals are classified into AA, A, B, C and D. ..

AA grade: the whole crystal is transparent inside and outside without defects, and the surface is free from man-made defects visible to the naked eye.

Grade A: There are tiny flaws, or tiny natural inclusions, clouds or flocs not exceeding 3mm.

Grade B: slightly flawed, and it is easy to see clouds or cotton wool with naked eyes.

Class C: There are large cloud-like inclusions, small ice cracks and small scratches on the surface.

Grade D: More than half of the whole crystal is cloud-like and inclusion, with large ice cracks and small cracks on the surface.

crystal

The conditions of crystal formation are more severe than the corresponding conditions. First of all, there needs to be enough stable growth space; Secondly, there should be hydrothermal solution rich in siliceous minerals, slightly alkaline and low salinity; Need low temperature (160℃-400℃) and medium pressure (2-3 atmospheres); It takes a certain growth time to meet these four conditions to generate crystals.

In nature, developed joints, cracks and faults are good spaces for crystal growth. Granite has strong development or metamorphism, which can provide sufficient hydrothermal solution and has good temperature and pressure. Time factor is easier to obtain, so the output of crystal is more extensive on the earth.

Crystals are often produced in the form of clusters and caves, among which caves generally exist in igneous rocks and basalts, with very thick lava flow layer formed by volcanic eruption. The dissolution of gas or hot water during volcanic eruption leads to a large number of pores in rocks. When the fluid rich in siliceous minerals enters the thin lava pores and the temperature and pressure conditions are suitable, crystals and other minerals will be precipitated.

Refer to the above contents: Baidu Encyclopedia-Rock Crystal, Baidu Encyclopedia-Crystal.