Question

How do geologists measure density of rock?

Answer 1

Rocks in nature can be found in different shapes, sizes and nature. This is due to an amazingly vast diversity of Earth. Now, while measuring the density of a rock, geologists first confirm the fact that the small piece of rock taken has the same composition of different elements and minerals as of the bigger piece of rock (ore). They then measure the density of rock by the standard method of mass and volume.

Complete answer:
Let us first assign some terms that we are going to use later in our problem. Let the mass of the rock be ‘M’ and the volume of rock be ‘V’.
Then, the density of the rock (say, D) can be calculated using the formula:
$\Rightarrow D=\dfrac{M}{V}$
Now, when an appropriate rock sample is selected by geologists, it is first of all weighted by a sensitive weighing machine. This gives us the mass (M) of the rock and was comparatively an easier process.
Then, we need to calculate the volume of rock. This is done by gently placing the rock in a well calibrated container filled with water or any other liquid that does not react with the rock and then noting the change in volume. This gives us the volume (V) of the rock. This process requires comparatively more precision than weighing the rock.
Therefore, now that we have the mass and volume of the sample rock, density can be calculated by putting their values in the following equation:
$\Rightarrow D=\dfrac{M}{V}$
Hence, the above represented method is the correct method that geologists apply to measure the density of rock.

Note:
The sample of rock selected for measures of density should not have any weathered surface structures as it may be affected when kept under water for calculation of volume displacement. Also, the rock should not be too small or too large as a small rock wouldn’t give the most accurate results and a large rock is harder to analyze.