Dolomite is a lime stone which contains carbonate of magnesia upto
Try it first: pick an option, then read the explanation.
Understanding Limestone and Dolomite
First, let's understand the basics. Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO₃). However, sometimes magnesium carbonate (MgCO₃) gets mixed in. The amount of magnesium carbonate determines the specific name of the rock.
Dolomite (also called Dolostone) is a type of limestone that is rich in magnesium. It's formed when the calcium ions in limestone are replaced by magnesium ions.
Detailed Analysis of Magnesium Content
D. 45%
This is the correct answer. For a rock to be classified as a true Dolomite (or Dolostone), it must contain a very high percentage of magnesium carbonate. Standard geological classifications state that Dolomite contains more than 40% and up to about 45.6% magnesium carbonate by weight. Therefore, 45% is the correct upper threshold among the given options.
A, B, C (15%, 25%, 35%)
Limestones with lower percentages of magnesium carbonate are given different names. While they are related to dolomite, they are not considered true dolomite rock.
- Magnesian Limestone: Contains 5% to 20% magnesium carbonate. The 15% option falls into this category.
- Dolomitic Limestone: Contains 20% to 40% magnesium carbonate. The 25% and 35% options fall into this category.
So, while a stone with 35% MgCO₃ is very "dolomitic," it isn't technically a full dolomite rock yet.
Summary: Limestone Classification by Magnesia Content
| Rock Name | Carbonate of Magnesia (MgCO₃) Content | Relevant Option(s) |
|---|---|---|
| Pure Limestone | < 5% | N/A |
| Magnesian Limestone | 5% - 20% | A. 15% |
| Dolomitic Limestone | 20% - 40% | B. 25%, C. 35% |
| Dolomite (Dolostone) | > 40% | D. 45% |
Study Tips
- Think "Maximum": When you see "Dolomite," think of the maximum amount of magnesia. It's the final stage of magnesium enrichment, so it will have the highest percentage.
- The 40% Rule: A simple rule of thumb is that once a limestone crosses the 40% threshold for magnesium carbonate, it earns the name "Dolomite."