Onyx Vs. Opal

Onyx is a very popular gemstone composed of silicon dioxide.^[1] Opal is also a very popular gemstone and its chemical composition is also silicon dioxide.^[2]

Quick Facts on Differences of Onyx and Opal

For a quick recap of the differences onyx and opal:

• While both onyx and opal can be translucent, onyx can be opaque and opal can be transparent.
• For chemical formulas, onyx is SiO2 while opal is SiO2· nH2O.
• While both onyx and opal can be vitreous or waxy, in terms of luster, opal can be pearly.
• Onyx can be commonly black while opal can be commonly red.
• Onyx's specific gravity is higher than opal - onyx is 2.651 and opal ranges from 1.98 to 2.25.

Quick Facts on Similarities of Onyx and Opal

The similarities of onyx and opal include:

• Onyx and opal both streak white.
• Onyx's rarity is similar to opal.

Summary of Onyx

Onyx is a mineral that belongs to the chalcedony family, which is a type of quartz that is formed by the deposition of silica in the cavities of rocks. It is a cryptocrystalline mineral, which means that its crystals are too small to be seen with the naked eye. Onyx is typically black, but it can also be found in other colors such as white, gray, brown, and green. It has a waxy luster and a smooth, polished surface.

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.

Table Comparison of Onyx vs Opal