RocksdayAnorthosite vs Marble
How to tell them apart
A pale rock made almost entirely of plagioclase feldspar — it makes up the Moon's bright highlands.
Photo: Mike Davis, CC0
Limestone recrystallized by heat and pressure into a mosaic of interlocking calcite grains.
Photo: Zyance, CC BY-SA 2.5
Quick tests
- Scratch glass: Anorthosite scratches glass (Mohs 6–6.5); Marble can't (Mohs 3–4).
- Acid (vinegar or dilute HCl): Marble fizzes; Anorthosite doesn't.
Key differences
- Marble fizzes and is much softer.
Side by side
| Property | Anorthosite | Marble |
|---|---|---|
| Type | Igneous rock | Metamorphic rock |
| Mohs hardness | 6–6.5 | 3–4 |
| Luster | Granular, glassy | Sugary sparkle |
| Colors | White, Gray | White, Gray, Pink, Green |
| Crystal system / structure | Coarse-grained | Interlocking crystals (non-foliated) |
| Specific gravity | 2.7–2.8 | 2.6–2.9 |
| Found in | Adirondack Mountains, New York; Nain, Labrador | Carrara, Italy; Yule, Colorado |
Properties that are the same for both are grayed out.
How to identify anorthosite
- Light gray to white, coarse feldspar.
- Few dark minerals.
- May flash blue like labradorite.
Structure: Coarse-grained
Full Anorthosite guide →How to identify marble
- Sparkly, sugary crystals on broken surfaces.
- Fizzes in acid.
- A knife scratches it.
- Often swirled or veined.
Structure: Interlocking crystals (non-foliated)
Full Marble guide →More comparisons
Could you tell them apart from a blurry close-up?
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