AllMineralsRock
Opal Vs. Tourmaline
Opal is a very popular gemstone composed of silicon dioxide.[1] Tourmaline is also a very popular gemstone and its chemical composition is boron silicate.[2]
Quick Facts on Differences of Opal and Tourmaline
For a quick recap of the differences opal and tourmaline:- While both opal and tourmaline can be translucent or transparent, tourmaline can be opaque.
- For chemical formulas, opal is SiO2· nH2O while tourmaline can be (Ca, Al, B)6O18(OH, Cr, F)4, Fe, Fe, K, Li, Mg, Mn)3(Al, Na)(Al or V)6(BO3)3(Si.
- While both opal and tourmaline can be vitreous, in terms of luster, opal can be pearly or waxy.
- Opal's rarity is less rare than tourmaline.
- Opal's specific gravity is lower than tourmaline - opal ranges from 1.98 to 2.25 and tourmaline ranges from 2.82 to 3.9.
Quick Facts on Similarities of Opal and Tourmaline
The similarities of opal and tourmaline include:- Opal and tourmaline both streak white.
- Opal and tourmaline both are red.
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 Tourmaline
Tourmaline is a mineral that belongs to the silicate group and is known for its unique crystal structure and the wide range of colors it comes in. It is a complex mineral that contains boron, aluminum, and other elements. Tourmaline is found in many different parts of the world, including Brazil, Afghanistan, Pakistan, and the United States. The mineral can be identified by its prismatic crystal habit, which means that it has a long, column-like shape with flat faces on either end.Table Comparison of Opal vs Tourmaline
| Opal (src) | Tourmaline (src) | |
|---|---|---|
| Transparency | transparent, translucent | transparent, translucent, opaque |
| Chemical Formula | SiO2· nH2O | (Ca,K,Na)(Al,Fe,Li,Mg,Mn)3(Al,Cr,Fe,V)6(BO3)3(Si,Al,B)6O18(OH,F)4 |
| Chemical Composition | silicon dioxide | boron silicate |
| Specific Gravity | 1.98, 2.25 | 2.82, 3.9 |
| Streak | white | white |
| Hydrous | Yes | No |
| Colors | common: red sometimes: blue, gray, pink, black, brown, green, white, orange, purple, yellow, colorless, band, multicolor |
common: red sometimes: blue, black less common: gray, pink, brown, green, white, orange, purple, violet, yellow, colorless, multicolor |
| Birefringence | none | δ = -0.018 to −0.040 |
| Fracture | conchoidal | conchoidal, uneven |