Identification guide · Minerals
How to Identify Borax
Borax is colorless to white or gray, sometimes with a yellowish or greenish tint from impurities, and has a vitreous to resinous, sometimes dull, luster with a white streak. It has a hardness of only 2 to 2.5 and one perfect cleavage direction, typically forming short prismatic crystals or granular and earthy masses in evaporite deposits. Its distinctly sweet alkaline taste and ready solubility in water separate it from harder, less soluble evaporite minerals like gypsum, though its tendency to dehydrate into powdery tincalconite on exposure to air is a key diagnostic behavior.
Borax identification checklist
| Color | White, Colorless, Gray | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous to resinous, earthy when dehydrated | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Transparent to translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 2–2.5 | 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, one direction | |
| Fracture | Conchoidal | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 1.7 | Noticeably light in the hand for its size (specific gravity about 1.7). |
| Crystal system | Monoclinic |
Extra tests for Borax
Glass check. Borax shares a glassy luster and conchoidal fracture with man-made glass. Glass sits near Mohs 5.5 and often contains round gas bubbles, so a hardness test and a hand lens separate them.
Borax look-alikes and how to tell them apart
Both sit near Mohs 2–2.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Borax vs Calcite →
Anhydrite is harder (Mohs 3–3.5) than Borax (Mohs 2–2.5), so Anhydrite will scratch Borax and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Borax vs Anhydrite →
Aragonite is harder (Mohs 3.5–4) than Borax (Mohs 2–2.5), so Aragonite will scratch Borax and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Borax vs Aragonite →
Celestine is harder (Mohs 3–3.5) than Borax (Mohs 2–2.5), so Celestine will scratch Borax and not the other way round. A fingernail (Mohs 2.5) scratches it easily.
Borax identification FAQ
How can you tell if a rock is Borax?
Check the color (white, colorless, and gray), the vitreous to resinous, earthy when dehydrated luster, a Mohs hardness of 2–2.5 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Borax?
Borax has a Mohs hardness of 2–2.5. A fingernail (Mohs 2.5) scratches it easily.
What is the difference between Borax and Calcite?
Borax (Mohs 2–2.5, vitreous to resinous, earthy when dehydrated luster) and Calcite (Mohs 3, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Borax vs Calcite comparison for a side-by-side table.
Is Borax worth anything?
Entry-level Borax specimens sell for around $2, typical collector pieces about $20, and premium examples $150 or more depending on size, quality and locality.
What color is Borax?
Borax is most often white, colorless, and gray. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
