Comparison · Sedimentary Rocks vs Quartz Family
Chert vs Quartz
Chert and Quartz are easy to confuse. Both sit near Mohs 6.5–7, 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 Chert and Quartz
- Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Luster is different: Chert is waxy to dull while Quartz is vitreous, greasy on fracture surfaces.
- Hold a thin edge to the light: Chert is Translucent to opaque, Quartz is Transparent to translucent.
- They overlap in gray, black, and brown, but Chert also comes in white, red, and green and Quartz also comes in clear, purple, yellow, and pink.
Chert vs Quartz properties
| Property | Chert | Quartz |
|---|---|---|
| Type | Sedimentary Rocks | Quartz Family |
| Mohs hardness | 6.5–7 | 7 |
| Luster | Waxy to dull | Vitreous, greasy on fracture surfaces |
| Streak | — | White |
| Transparency | Translucent to opaque | Transparent to translucent |
| Specific gravity | 2.6–2.65 | 2.65 |
| Crystal system | — | Trigonal |
| Common colors | Gray, White, Black, Brown, Red, Green | Colorless, White, Purple (amethyst), Yellow (citrine), Pink (rose), Brown/black (smoky) |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $5–$250+ |
Which is more valuable?
Quartz is usually the more valuable of the two: a typical collector specimen runs about $35 against $10 for Chert, and premium Quartz can reach $250 or more.
About Chert
Chert is a hard, fine-grained sedimentary rock composed almost entirely of microcrystalline or cryptocrystalline quartz, formed either by direct chemical precipitation of silica or by the accumulation and diagenetic alteration of silica-secreting organisms like radiolarians and diatoms. It breaks with a distinctive conchoidal fracture that produces sharp edges, a property that made it invaluable to prehistoric toolmakers. Chert occurs in nodules within limestone and chalk or as bedded layers, and its color varies widely depending on trace mineral impurities.
About Quartz
Quartz is silicon dioxide, SiO2, one of the most abundant minerals in Earth's continental crust, crystallizing in the trigonal division of the hexagonal crystal system with a hardness of 7 that makes it a standard reference point on the Mohs scale. Its six-sided prismatic crystals, often terminated by pyramidal points, are among the most recognizable crystal shapes in mineralogy. Quartz occurs in nearly every rock type and geologic setting, from granite pegmatites to sedimentary sandstones to hydrothermal veins.
Chert vs Quartz FAQ
Is Chert the same as Quartz?
No. Chert is a sedimentary rock while Quartz is a quartz family. Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Chert from Quartz?
Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Luster is different: Chert is waxy to dull while Quartz is vitreous, greasy on fracture surfaces. Hold a thin edge to the light: Chert is Translucent to opaque, Quartz is Transparent to translucent.
Which is harder, Chert or Quartz?
They are about equally hard, both near Mohs 6.5–7.
Which is more valuable, Chert or Quartz?
Quartz is usually the more valuable of the two: a typical collector specimen runs about $35 against $10 for Chert, and premium Quartz can reach $250 or more.
