Opal and metamorphic rocks are gems made of mineral chrysoberyl (hardness 8.5, density 4.72g/cm3). Therefore, their main chemical composition is the same, and they are all BeAl2O4, but the trace components are different. Opals generally contain trace amounts of iron, while metamorphic rocks generally contain trace amounts of chromium.

The most important thing is to distinguish opal from other gems with cat's eye effect. The difference between opal and cat's eye effect is still a basic concept. Whether natural or synthetic, there are many gems that can show cat's eye effect, such as tourmaline and Yishi. But these gems with cat's eye effect are not opals, and their correct names are "gem names+cat's eyes", such as quartz cat's eyes.

Quality evaluation The bigger the opal, the harder it is, so the weight is one of the basic factors to evaluate opal. More importantly, color, eyeliner and uniformity are also important.

The best color of opal is very strong yellow-green, brown-yellow and honey-yellow, followed by green and then slightly dark brown. Very white yellow and very white green have lower value. The worst are variegated and gray.

The best opal eyeliner should be narrow, with clear boundaries and vivid light, and should be located in the center of the gem. It is important that the eyeliner should be in contrast with the background and clean. The bigger the eyes, the better. Be sharp together. On the one hand, the value of variable stone depends on its perfection and cutting and grinding technology, but more importantly, it depends on the color and luster of gemstones. In the sun, the more colors, the more beautiful. Under non-natural light, the closer the color is to ruby, the better. But in fact, few people can achieve this effect, most of the colors are just similar, and more metamorphic rocks are red like garnet and green like tourmaline, and they change a lot. Metamorphic rocks with good color change and uniform appearance belong to the advanced category.

Crystal (crystal)

The chemical composition of the basic characteristic crystal is SiO2, and the crystal surface always presents horizontal stripes, which is the most important feature and basis for identifying the original crystal stone. The hardness is 7 and the density is 2.65g/cm3.

Variation crystal characteristics

Colorless crystal: colorless and transparent crystal, without cracks and inclusions. Colorless crystals are mostly used for making necklaces and carving crafts, the most famous of which is the crystal ball. According to ancient legends, there are gods hidden in the crystal ball. Staring at it can predict the future or see the distant situation. Crystal has a characteristic: holding a crystal in your hand makes you feel very cold.

Amethyst: amethyst for short, not only purple, but also purple transparent crystal. According to ancient legend, amethyst has magical ability, which can bring happiness and longevity to its owner, ward off evil spirits and prevent homesickness. If amethyst is brought to the banquet, it can also prevent people from getting drunk.

Smoke crystal, tea crystal and ink crystal: This is a series of crystal colors from shallow to deep. The color of this series of crystals is a mixture of extremely fine and evenly distributed carbon elements in the crystals. Mainly used for necklaces and glasses grinding, but the price is not too high.

Hair crystal: it is a transparent crystal, containing needle-like, hairy and fibrous mineral inclusions, including rutile, tourmaline, amphibole, asbestos and actinolite. In a word, hair crystal is an excellent raw material for handicrafts.

Barasuishou: In most cases, pink crystals are not only poor in crystal form, but also full of cracks. Mainly used as raw materials for carving handicrafts, jade carving firms call it hibiscus stone. It is also often used to make necklaces.

Quartz cat's eye and starlight: crystals with cat's eye and starlight effects are more expensive than ordinary crystals.

Distinction between true and false

1. Difference from synthetic crystal: Synthetic crystal is more expensive than ordinary rock crystal, so there is no need for authenticity identification. However, if the diameter of crystal ball and amethyst is larger than 10 cm, natural amethyst is far more expensive than synthetic crystal, so it should be correctly identified. In terms of raw materials, natural amethyst has a regular external crystal shape, while synthetic amethyst has no crystal shape, and a flaky crystal nucleus can be seen in the center. For the finished product, natural amethyst.

2. Difference from glass: Because the hardness of glass is lower than that of crystal, crystal can always carve glass, but glass can't carve crystal; Because of the high thermal conductivity of crystal, it feels very cold, while glass doesn't.

Quality evaluation

The most important thing that affects crystal is color. From the jewelry market, the most popular crystal is purple, so the price of amethyst should be the highest. But also has the effects of starlight and cat's eye, with good effect and high value. In addition, some crystals with inclusions and special shapes, such as mountains, water, flowers, birds, figures and characters, are very rare ornamental stones.