Identification guide · Silicate Minerals
How to Identify Kaolinite
Kaolinite is usually white, cream, and pale yellow with a earthy luster and is opaque. It has a Mohs hardness of 2. A fingernail (Mohs 2.5) scratches it easily. Its streak is white. It is most often confused with Limestone, Bauxite, and Chalk; the tests below separate them.
Kaolinite identification checklist
| Color | White, Cream, Pale yellow, Light gray | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Earthy | Compare a fresh surface with glass and metal; this luster is softer than either. |
| Transparency | Opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 2 | A fingernail (Mohs 2.5) scratches it easily. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect basal | |
| Fracture | Earthy | |
| Specific gravity | 2.6 | Ordinary rock-like heft (specific gravity about 2.6), similar to quartz. |
| Crystal system | Triclinic |
Kaolinite look-alikes and how to tell them apart
Limestone is harder (Mohs 3) than Kaolinite (Mohs 2), so Limestone will scratch Kaolinite and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Kaolinite vs Limestone →
Both sit near Mohs 2, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Kaolinite vs Bauxite →
Both sit near Mohs 2, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Kaolinite vs Chalk →
Both sit near Mohs 2, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Field tips
- Look for a soft, white to cream earthy mineral that feels powdery and may stick slightly to the tongue.
- Kaolinite often gives off an earthy clay smell when breathed on or dampened.
- Distinguish it from talc by its earthy rather than soapy feel and from chalk by its lack of reaction to acid.
Kaolinite identification FAQ
How can you tell if a rock is Kaolinite?
Check the color (white, cream, pale yellow, and light gray), the earthy luster, a Mohs hardness of 2 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Kaolinite?
Kaolinite has a Mohs hardness of 2. A fingernail (Mohs 2.5) scratches it easily.
What is the difference between Kaolinite and Limestone?
Kaolinite (Mohs 2, earthy luster) and Limestone (Mohs 3, dull luster) look alike, but hardness, streak and heft usually separate them. See the full Kaolinite vs Limestone comparison for a side-by-side table.
Is Kaolinite worth anything?
Entry-level Kaolinite specimens sell for around $2, typical collector pieces about $15, and premium examples $80 or more depending on size, quality and locality.
What color is Kaolinite?
Kaolinite is most often white, cream, pale yellow, and light gray. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
