AllMineralsRock
Opal Vs. Pearl
Opal is a very popular gemstone composed of silicon dioxide.[1] Pearl is also a very popular gemstone and its chemical composition is calcium carbonate.[2]
Quick Facts on Differences of Opal and Pearl
For a quick recap of the differences opal and pearl:- While both opal and pearl can be translucent, opal can be transparent and pearl can be opaque.
- For chemical formulas, opal is SiO2· nH2O while pearl is CaCO3.
- While both opal and pearl can be pearly, in terms of luster, opal can be vitreous or waxy and pearl can be dull.
- Opal can be commonly red while pearl can be commonly cream or white.
- Opal's rarity is less rare than pearl.
- Opal's specific gravity is lower than pearl - opal ranges from 1.98 to 2.25 and pearl ranges from 2.6 to 2.72.
Quick Facts on Similarities of Opal and Pearl
The similarities of opal and pearl include:- Opal and pearl both streak white.
Summary of Opal
Opal is a mineraloid that is formed from the silica-rich water that permeates through the earth's crust. It is a beautiful gemstone that is known for its unique play of colors. Opal is a non-crystalline mineral that is made up of tiny spheres of silica, which diffract light in a way that creates a rainbow of colors. The colors of opal can range from white, gray, and black to red, orange, yellow, green, blue, and purple.Summary of Pearl
Pearl is a mineral that is formed within the shells of certain mollusks, particularly oysters and mussels. It is a hard, round, lustrous object that is highly prized for its beauty and rarity. Pearls are formed when a foreign object, such as a grain of sand or a piece of shell, enters the mollusk and irritates its soft tissue. The mollusk then secretes a substance called nacre around the irritant, layer upon layer, until a pearl is formed.Table Comparison of Opal vs Pearl
| Opal (src) | Pearl (src) | |
|---|---|---|
| Transparency | transparent, translucent | translucent, opaque |
| Chemical Formula | SiO2· nH2O | CaCO3 |
| Chemical Composition | silicon dioxide | calcium carbonate |
| Specific Gravity | 1.98, 2.25 | 2.6, 2.72, 2.78, 2.78, 2.85 |
| Streak | white | white |
| Hydrous | Yes | No |
| Colors | common: red sometimes: blue, gray, pink, black, brown, green, white, orange, purple, yellow, colorless, band, multicolor |
common: cream, white sometimes: red less common: blue, gold, gray, pink, black, brown, green, orange, purple, silver, yellow, iridescent, multicolor |
| Birefringence | none | δ = 0.156 |
| Fracture | conchoidal | uneven |