Comparison · Quartz Family vs Minerals
Agate vs Onyx
Agate and Onyx are easy to confuse. Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Agate and Onyx
- Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Luster is different: Agate is waxy while Onyx is waxy to vitreous.
- Hold a thin edge to the light: Agate is translucent, Onyx is Translucent to opaque.
- They overlap in multicolored, brown, and red, but Agate also comes in blue, green, and gray and Onyx also comes in black and white.
- Well-formed crystals give it away: Agate is hexagonal, Onyx is Trigonal (cryptocrystalline).
Agate vs Onyx properties
| Property | Agate | Onyx |
|---|---|---|
| Type | Quartz Family | Minerals |
| Mohs hardness | 7 | 6.5–7 |
| Luster | waxy | Waxy to vitreous |
| Streak | White | White |
| Transparency | translucent | Translucent to opaque |
| Specific gravity | 2.6 | 2.6–2.65 |
| Crystal system | hexagonal | Trigonal (cryptocrystalline) |
| Common colors | Banded, Blue, Brown, Red, Green, Gray | Black and white banded, Brown and white banded, Red and white banded |
| Rarity | common | common |
| Typical specimen value | $5–$300+ | $2–$150+ |
Which is more valuable?
Agate is usually the more valuable of the two: a typical collector specimen runs about $25 against $20 for Onyx, and premium Agate can reach $300 or more.
About Agate
Agate is a banded variety of chalcedony formed in concentric layers in volcanic rocks. Each layer represents a different period of mineral deposition.
About Onyx
Onyx is a banded variety of chalcedony, a cryptocrystalline form of quartz, distinguished from agate by its straight, parallel bands rather than agate's characteristically curved layers. Most commercial onyx sold in black and white banded slabs is actually dyed to enhance contrast, since naturally occurring true onyx with strong black-and-white banding is relatively uncommon. Chemically identical to other quartz varieties, onyx owes its distinctive look entirely to microscopic banding formed during slow silica deposition.
Agate vs Onyx FAQ
Is Agate the same as Onyx?
No. Agate is a quartz family while Onyx is a mineral. Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Agate from Onyx?
Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Luster is different: Agate is waxy while Onyx is waxy to vitreous. Hold a thin edge to the light: Agate is translucent, Onyx is Translucent to opaque.
Which is harder, Agate or Onyx?
They are about equally hard, both near Mohs 7.
Which is more valuable, Agate or Onyx?
Agate is usually the more valuable of the two: a typical collector specimen runs about $25 against $20 for Onyx, and premium Agate can reach $300 or more.
