Onyx and obsidian are both dark, captivating stones often used in jewelry and decorative objects. Their similar appearances often lead to confusion, but understanding their geological origins and physical properties reveals distinct differences. This comprehensive guide will explore the key distinctions between onyx and obsidian, answering common questions and helping you appreciate the unique beauty of each.
What is Onyx?
Onyx is a banded variety of chalcedony, a microcrystalline form of quartz. This means it's composed of extremely fine quartz crystals, creating a smooth, waxy texture. The defining characteristic of onyx is its parallel bands of contrasting colors, most famously black and white, but also featuring variations with browns, reds, and even greens. These bands are created during the stone's formation, a process involving the deposition of silica in layers within cavities or fissures.
What is Obsidian?
Obsidian, unlike onyx, is a volcanic glass. It forms when felsic lava cools rapidly, preventing the formation of mineral crystals. This rapid cooling results in a glassy texture and a distinctive conchoidal fracture (a curved, shell-like break). Obsidian is typically black, although variations can occur depending on mineral inclusions, resulting in colors like brown, green, or even iridescent shades.
Key Differences Between Onyx and Obsidian: A Comparison
Here's a table summarizing the key differences:
| Feature | Onyx | Obsidian |
|---|---|---|
| Composition | Microcrystalline quartz (chalcedony) | Volcanic glass |
| Formation | Sedimentary deposition in cavities | Rapid cooling of felsic lava |
| Texture | Smooth, waxy | Glassy, brittle |
| Typical Color | Black and white banded, other colors | Black, brown, green, iridescent |
| Hardness | 6.5-7 on the Mohs scale | 5-5.5 on the Mohs scale |
| Fracture | Conchoidal (but less pronounced) | Highly distinctive conchoidal fracture |
How Can You Tell Onyx and Obsidian Apart?
While both stones can be black, several key features help differentiate them:
- Bands: Onyx typically displays distinct, parallel bands of color. Obsidian rarely shows banding; its color is generally consistent throughout.
- Texture: Feel the stone. Onyx has a smoother, slightly waxy texture, while obsidian feels glassy and more brittle.
- Fracture: If you see a broken edge, obsidian exhibits a very characteristic, curved conchoidal fracture. Onyx’s fracture is also conchoidal but less pronounced and less curved.
- Luster: Onyx generally has a more subtle luster, while obsidian can display a strong vitreous (glassy) luster.
What are the Uses of Onyx and Obsidian?
Both onyx and obsidian have been prized for their beauty and used for centuries in various applications:
- Jewelry: Both are popular in rings, pendants, earrings, and bracelets.
- Ornamental objects: Used to create decorative items such as carvings, vases, and figurines.
- Intaglio carvings: Onyx's ability to take a fine polish makes it suitable for intricate carvings.
- Tools: In ancient times, obsidian's sharp edges were utilized to create tools and weapons.
What is the difference in hardness between Onyx and Obsidian?
Onyx is harder than obsidian, scoring 6.5-7 on the Mohs hardness scale compared to obsidian's 5-5.5. This means onyx is more resistant to scratches and wear.
Is obsidian more valuable than onyx?
The value of both stones depends on several factors, including color, clarity, quality of cut and polish, and overall size. While generally obsidian is less expensive than high-quality onyx, some rare obsidian varieties, like rainbow obsidian, can command high prices.
This comprehensive comparison of onyx and obsidian should equip you with the knowledge to distinguish between these two captivating gemstones. Remember to always handle these stones with care due to their varying degrees of fragility.
