RocksdayCalcite vs Sulfur
How to tell them apart
One of the most common minerals on Earth and the main ingredient of limestone and marble. It breaks into perfect slanted boxes (rhombs) and fizzes in acid.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
A native element that crystallizes around volcanic vents and in salt domes. Unmistakably bright yellow.
Photo: Ivar Leidus, CC BY-SA 4.0
Quick tests
- Fingernail: A fingernail scratches Sulfur (Mohs 1.5–2.5) but not Calcite (Mohs 3).
- Acid (vinegar or dilute HCl): Calcite fizzes; Sulfur doesn't.
- Streak (rub on unglazed porcelain): Calcite leaves a white streak; Sulfur leaves white to pale yellow.
- Heft: Calcite feels noticeably heavier for its size (specific gravity 2.71 vs 2.07).
Key differences
- Yellow calcite is harder, fizzes in acid and has no smell.
Side by side
| Property | Calcite | Sulfur |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 3 | 1.5–2.5 |
| Luster | Vitreous | Resinous |
| Streak | White | White to pale yellow |
| Colors | Clear, White, Orange, Yellow, Blue, Green | Yellow |
| Crystal system | Trigonal | Orthorhombic |
| Specific gravity | 2.71 | 2.07 |
| Formula | CaCO₃ | S |
| Found in | Iceland; Chihuahua, Mexico | Kawah Ijen, Indonesia; Agrigento, Sicily |
Properties that are the same for both are grayed out.
How to identify calcite
- Fizzes in cold dilute hydrochloric acid (or slowly in vinegar).
- Breaks into rhomb-shaped pieces along three cleavage planes.
- Hardness 3 — a copper coin barely scratches it, a knife easily does.
- Clear pieces show double images of text underneath.
Crystal system: Trigonal
Full Calcite guide →How to identify sulfur
- Bright lemon yellow.
- Very light and soft.
- Smells like rotten matches when warmed or rubbed.
- Melts and burns with a blue flame.
Crystal system: Orthorhombic
Full Sulfur guide →More comparisons
Could you tell them apart from a blurry close-up?
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