How is specific gravity defined in minerals?

Specific gravity is defined as the ratio of the weight of a given volume of a mineral to the weight of an equal volume of water at a specified temperature (usually 4 degrees Celsius, where water reaches its maximum density). This measurement is essential in mineralogy and geology as it provides a way to compare the density of different minerals relative to water, which is a standard reference.

This definition highlights the relationship between the mass and volume of the mineral relative to water, allowing for easier identification and characterization of minerals based on their physical properties. Since water is commonly used as the baseline, specific gravity becomes a convenient and widely used parameter in various scientific fields, particularly in mining engineering and geology.

The other options do not accurately describe specific gravity: comparing minerals to air does not provide a direct measurement against a standard medium, while the volume of a mineral per square unit and total mass per unit volume pertain more to general density rather than the specific gravity calculation.