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Alexandrite Vs. Sapphire
Alexandrite is an uncommon gemstone composed of beryllium aluminate with chromium.[1] Sapphire is a very popular gemstone and its chemical composition is silicon dioxide.[2]
Quick Facts on Differences of Alexandrite and Sapphire
For a quick recap of the differences alexandrite and sapphire:- In terms of crystallography, alexandrite is orthorhombic while sapphire can be hexagonal or trigonal.
- For chemical formulas, alexandrite is BeAl2O4 while sapphire is Al2O3.
- While both alexandrite and sapphire is vitreous, in terms of luster, sapphire can be adamantine.
- While both alexandrite and sapphire can be commonly green, sapphire is often blue.
- Alexandrite's hardness is lower than sapphire - alexandrite is 8.5 and sapphire is 9 on the Moh's scale.
- Alexandrite's specific gravity is lower than sapphire - alexandrite ranges from 3.68 to 3.8 and sapphire ranges from 3.99 to 4.
Quick Facts on Similarities of Alexandrite and Sapphire
The similarities of alexandrite and sapphire include:- Alexandrite and sapphire both can be opaque, translucent or transparent.
- Alexandrite and sapphire both streak colorless.
- Alexandrite's rarity is similar to sapphire.
Summary of Alexandrite
Alexandrite is a rare and highly valued mineral that belongs to the chrysoberyl family. It is known for its unique color-changing properties, which can range from green or blue-green in daylight to purplish-red in incandescent light. This phenomenon is called pleochroism, and it is caused by the mineral's composition, which includes traces of chromium.Summary of Sapphire
Sapphire is a precious mineral that belongs to the corundum family. It is a variety of aluminum oxide that is distinguished by its blue color, although it can also be found in other colors such as pink, yellow, green, and purple. Sapphire is one of the hardest minerals in the world, with a hardness of 9 on the Mohs scale, making it an ideal material for use in jewelry and industrial applications.Table Comparison of Alexandrite vs Sapphire
| Alexandrite (src) | Sapphire (src) | |
|---|---|---|
| Transparency | transparent, translucent, opaque | transparent, translucent, opaque |
| Chemical Formula | BeAl2O4 | Al2O3 |
| Chemical Composition | beryllium aluminate with chromium | silicon dioxide |
| Specific Gravity | 3.68, 3.8 | 3.99, 4, 4.1 |
| Hardness | 8.5 | 9 |
| Streak | colorless | colorless |
| Crystallography | orthorhombic | hexagonal, trigonal |
| Refractive Index | 1.745, 1.759 | 1.757, 1.779 |
| Hydrous | No | No |
| Colors | common: green sometimes: red, blue, purple less common: gray, pale, pink, violet, yellow, multicolor |
common: green, blue sometimes: pink, amber, yellow less common: gray, black, brown, white, orange, purple, violet, colorless, red, gold, multicolor |
| Fracture | conchoidal, uneven | conchoidal |