Comparison · Quartz Family vs Silicate Minerals
Quartz vs Sillimanite
Quartz and Sillimanite 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 Quartz and Sillimanite
- Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Sillimanite feels noticeably heavier for its size (specific gravity 3.24 versus 2.65 for Quartz).
- Hold a thin edge to the light: Quartz is Transparent to translucent, Sillimanite is transparent.
- They overlap in yellow, gray, and brown, but Quartz also comes in clear, purple, pink, and black and Sillimanite also comes in white and green.
- Well-formed crystals give it away: Quartz is Trigonal, Sillimanite is orthorhombic.
Quartz vs Sillimanite properties
| Property | Quartz | Sillimanite |
|---|---|---|
| Type | Quartz Family | Silicate Minerals |
| Mohs hardness | 7 | 7 |
| Luster | Vitreous, greasy on fracture surfaces | vitreous |
| Streak | White | White |
| Transparency | Transparent to translucent | transparent |
| Specific gravity | 2.65 | 3.24 |
| Crystal system | Trigonal | orthorhombic |
| Common colors | Colorless, White, Purple (amethyst), Yellow (citrine), Pink (rose), Brown/black (smoky) | White, Gray, Brown, Pale green, Yellow |
| Rarity | common | uncommon |
| Typical specimen value | $5–$250+ | $10–$450+ |
Which is more valuable?
Sillimanite is usually the more valuable of the two: a typical collector specimen runs about $70 against $35 for Quartz, and premium Sillimanite can reach $450 or more.
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.
About Sillimanite
Sillimanite is an aluminum silicate mineral that forms slender prismatic crystals or fibrous masses, the fibrous variety being called fibrolite. It is one of three aluminosilicate minerals that share the same composition but differ in structure.
Quartz vs Sillimanite FAQ
Is Quartz the same as Sillimanite?
No. Quartz is a quartz family while Sillimanite is a silicate 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 Quartz from Sillimanite?
Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Sillimanite feels noticeably heavier for its size (specific gravity 3.24 versus 2.65 for Quartz). Hold a thin edge to the light: Quartz is Transparent to translucent, Sillimanite is transparent.
Which is harder, Quartz or Sillimanite?
They are about equally hard, both near Mohs 7.
Which is more valuable, Quartz or Sillimanite?
Sillimanite is usually the more valuable of the two: a typical collector specimen runs about $70 against $35 for Quartz, and premium Sillimanite can reach $450 or more.
