Which of the following is the hardest natural substance on Earth?

Which of these is an example of an igneous rock?

Which mineral is the main source of iron?

Which of the following is a metamorphic rock?

Which scale is used to measure the hardness of minerals?

Which of these is the main component of limestone?

Coal is formed from which type of material?

Which of the following pairs is correctly matched?

The parent rock of marble is:

Which mineral is commonly used in making cement?