Comparison · Sedimentary Rocks
Dolomite vs Marl
Dolomite and Marl are easy to confuse because both are sedimentary rocks. Dolomite is harder (Mohs 3.5–4) than Marl (Mohs 2.5), so Dolomite will scratch Marl 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 Dolomite and Marl
- Dolomite is harder (Mohs 3.5–4) than Marl (Mohs 2.5), so Dolomite will scratch Marl and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
- Streak color differs: Dolomite leaves a white streak on unglazed porcelain, Marl leaves white to light gray.
- Luster is different: Dolomite is vitreous to dull while Marl is dull.
- Hold a thin edge to the light: Dolomite is Opaque, Marl is opaque.
- They overlap in white, gray, and brown, but Dolomite also comes in pink and yellow and Marl also comes in green.
Dolomite vs Marl properties
| Property | Dolomite | Marl |
|---|---|---|
| Type | Sedimentary Rocks | Sedimentary Rocks |
| Mohs hardness | 3.5–4 | 2.5 |
| Luster | Vitreous to dull | dull |
| Streak | White | White to light gray |
| Transparency | Opaque | opaque |
| Specific gravity | 2.8–2.9 | 2.4 |
| Crystal system | — | varies |
| Common colors | White, Gray, Pink, Brown, Yellow | Gray, Cream, White, Tan, Greenish gray |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $1–$75+ |
Which is more valuable?
Typical specimens of Dolomite and Marl trade in a similar range, around $10.
About Dolomite
Dolomite refers both to the mineral calcium magnesium carbonate, CaMg(CO3)2, and to dolostone, the sedimentary rock composed largely of that mineral. Dolostone typically forms when magnesium-rich water alters existing limestone after deposition, replacing some of the original calcium with magnesium in a process still actively studied by geologists. The rock is usually pale gray, tan, or pinkish and weathers into rounded, pitted outcrops distinct from sharper limestone cliffs.
About Marl
Marl is an earthy sedimentary rock or sediment made of mixed clay and calcium carbonate. It often looks gray, cream, tan, or soft and chalky.
Dolomite vs Marl FAQ
Is Dolomite the same as Marl?
No. Both are sedimentary rocks, but they are distinct rock types with different hardness, streak or luster. Dolomite is harder (Mohs 3.5–4) than Marl (Mohs 2.5), so Dolomite will scratch Marl and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
How can you tell Dolomite from Marl?
Dolomite is harder (Mohs 3.5–4) than Marl (Mohs 2.5), so Dolomite will scratch Marl and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Streak color differs: Dolomite leaves a white streak on unglazed porcelain, Marl leaves white to light gray. Luster is different: Dolomite is vitreous to dull while Marl is dull.
Which is harder, Dolomite or Marl?
Dolomite is harder: Mohs 3.5–4 against Mohs 2.5 for Marl.
Which is more valuable, Dolomite or Marl?
Typical specimens of Dolomite and Marl trade in a similar range, around $10.
