Comparison · Minerals vs Carbonates
Calcite vs Siderite
Calcite and Siderite are easy to confuse. Siderite is harder (Mohs 4) than Calcite (Mohs 3), so Siderite will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Calcite and Siderite
- Siderite is harder (Mohs 4) than Calcite (Mohs 3), so Siderite will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
- Siderite feels noticeably heavier for its size (specific gravity 3.96 versus 2.7 for Calcite).
- Hold a thin edge to the light: Calcite is transparent, Siderite is translucent.
- They overlap in yellow, but Calcite also comes in clear, orange, blue, green, and pink and Siderite also comes in brown and gray.
Calcite vs Siderite properties
| Property | Calcite | Siderite |
|---|---|---|
| Type | Minerals | Carbonates |
| Mohs hardness | 3 | 4 |
| Luster | vitreous | vitreous |
| Streak | White | White |
| Transparency | transparent | translucent |
| Specific gravity | 2.7 | 3.96 |
| Crystal system | trigonal | trigonal |
| Common colors | Colorless, White, Yellow, Orange, Blue, Green, Pink | Yellowish brown, Brown, Tan, Gray |
| Rarity | common | common |
| Typical specimen value | $2–$100+ | $5–$350+ |
Which is more valuable?
Siderite is usually the more valuable of the two: a typical collector specimen runs about $45 against $15 for Calcite, and premium Siderite can reach $350 or more.
About Calcite
Calcite is one of the most common minerals on Earth, found in sedimentary, metamorphic, and igneous rocks. It's the primary component of limestone and marble.
About Siderite
Siderite is an iron carbonate mineral that occurs as honey-brown to tan rhombohedral crystals, often with curved or saddle-shaped faces. It also forms massive and concretionary masses and is a recognized iron ore.
Calcite vs Siderite FAQ
Is Calcite the same as Siderite?
No. Calcite is a mineral while Siderite is a carbonate. Siderite is harder (Mohs 4) than Calcite (Mohs 3), so Siderite will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
How can you tell Calcite from Siderite?
Siderite is harder (Mohs 4) than Calcite (Mohs 3), so Siderite will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Siderite feels noticeably heavier for its size (specific gravity 3.96 versus 2.7 for Calcite). Hold a thin edge to the light: Calcite is transparent, Siderite is translucent.
Which is harder, Calcite or Siderite?
Siderite is harder: Mohs 4 against Mohs 3 for Calcite.
Which is more valuable, Calcite or Siderite?
Siderite is usually the more valuable of the two: a typical collector specimen runs about $45 against $15 for Calcite, and premium Siderite can reach $350 or more.
