Emerald

Synthetic Corundum - According to different sources, corundum can be divided into two types: natural corundum and artificial corundum. Natural corundum is a corundum mineral, while artificial corundum is artificially synthesized. The main differences between the two are:

**Different formation methods:**

Artificial corundum is a synthetic alumina material prepared under high temperature and high pressure conditions. Natural corundum is formed naturally and after geological processes, and is commonly found in deserts or giant rocks.

**Different chemical compositions:**

The main components of artificial corundum and natural corundum are aluminum oxide. Natural corundum is affected by various chemical elements during the formation process and has more impurities, resulting in different colors and chemical compositions; artificial corundum can have a chemical composition of nearly 100% % alumina, there are also products such as brown corundum and black corundum containing impurities.

Corundum is a rock-forming mineral formed from the crystallization of aluminum oxide (Al2O3). Corundum often contains small amounts of iron, titanium, vanadium and chromium ions. Pure aluminum oxide crystals are colorless, but corundum appears in different colors due to different impurities.

Among gem-grade corundum, corundum mixed with metallic chromium is bright red in color and is generally called ruby; while blue or colorless corundum is generally classified as sapphire. The English name "corundum" of corundum originates from "Kurundam" in "Tamil", which originates from Kuruvinda in "Sanskrit", which means "ruby".

**synthetic corundum**

In 1837, Marc Antoine Gaudin used a small amount of chromium as a pigment and melted aluminum oxide at high temperature, thus obtaining synthetic corundum for the first time. In 1847, Jacques-Joseph Hébelmont obtained white synthetic corundum by melting aluminum oxide in boric acid. In 1877, Frimy and Auguste Verneuil obtained artificial rubies by sintering barium fluoride, aluminum oxide and a small amount of chromium at a high temperature of more than 2,000 degrees. In 1903 Verneuil claimed that he could produce rubies on a commercial scale using this method.

**Specifications:**

**Crystal structure: ** It belongs to the trigonal crystal system.

**Hardness: ** Mohs hardness of 9, second only to diamond, is also a very hard substance in nature; like diamond, its hardness also has anisotropy.

**Density:** The density is relatively high, 3.95~4.10g/cm3.

**Cleavage and cleavage:** No cleavage, but cleavage in four different directions. Because they are often cracked, red and sapphire are also afraid of impact.

**Luster:** Glass luster to quasi-adamantine luster, weaker than diamond.

**Refractive index and birefringence:** Corundum is a birefringent mineral, also called optical heterogeneity: the maximum refractive index is 1.770, the minimum is 1.762, and the birefringence is not large, only 0.008.

**Dichroism:** Corundum is a heterogeneous mineral with "dichroism" (also called pleochroism). The pleochroism of corundum is medium, with rubies showing purple-red/orange-red and sapphires showing purple-blue/green-blue. Differences in color can be seen with a polarizing microscope or a simple "dichroic mirror", a small instrument.

**Fluorescence:** Ruby can fluoresce red under ultraviolet light, which can be used to distinguish red garnet (non-fluorescent). Sapphire usually does not emit light.

**Advantages:**

Jewelry use: Colorful and transparent or translucent crystals can be used as gemstones. Both ruby and sapphire are corundum minerals. In addition to the starlight effect, only translucent-transparent and brightly colored corundum can be used as gemstones. The red ones are called rubies, while the other shades of corundum are commercially known as sapphires.