Identification guide · Borate Minerals
How to Identify Ulexite
Ulexite is usually white and colorless with a vitreous luster and is translucent. It has a Mohs hardness of 2.5. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Its streak is white. It is most often confused with Calcite, Borax, and Gypsum; the tests below separate them.
Ulexite identification checklist
| Color | White, Colorless | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 2.5 | A copper coin (Mohs 3.5) scratches it, but a fingernail does not. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect | |
| Fracture | Uneven | |
| Specific gravity | 1.95 | Noticeably light in the hand for its size (specific gravity about 1.95). |
| Crystal system | Triclinic |
Ulexite look-alikes and how to tell them apart
Both sit near Mohs 2.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Ulexite vs Calcite →
Both sit near Mohs 2.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Ulexite vs Borax →
Both sit near Mohs 2.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Ulexite vs Gypsum →
Both sit near Mohs 2.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Field tips
- Look for silky white fibrous masses or nodules that are very light in the hand.
- Fibrous slices that project an image from below are nearly diagnostic of ulexite.
- Low hardness near 2.5 and a low specific gravity support identification.
Ulexite identification FAQ
How can you tell if a rock is Ulexite?
Check the color (white and colorless), the vitreous luster, a Mohs hardness of 2.5 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Ulexite?
Ulexite has a Mohs hardness of 2.5. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
What is the difference between Ulexite and Calcite?
Ulexite (Mohs 2.5, vitreous luster) and Calcite (Mohs 3, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Ulexite vs Calcite comparison for a side-by-side table.
Is Ulexite worth anything?
Entry-level Ulexite specimens sell for around $5, typical collector pieces about $25, and premium examples $120 or more depending on size, quality and locality.
What color is Ulexite?
Ulexite is most often white and colorless. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
