This is the specific gravity of the mineral. It's a comparison of how much mass a given volume of it has compared to the mass of an equal volume of water.
It does not. It equals volume. The weight will vary depending on the substance occupying that volume.
volume and weight
Compare its weight to the weight of an equal volume of water. The weight of the specimen divided by the weight of the water equals the density of the specimen.
Height and diameter will give you the volume, if you know the density you can then calculate weight from that.
If the sample is homogeneous, then half of its volume has half of its mass and half of its weight.
Mineral density should know. Weight / density = volume
The density of a pure mineral is measured using various apparatus and techniques which are covered in most mineralogy textbooks.
Specific gravity
Percent of an objects mass is expressed in terms of its weight. Percent of an objects volume is expressed in terms of its size.
The density of minerals is a measure of weight vs volume of the mineral. See related links for more details.
Grams & milligrams measure weight, not volume. For measuring volume, use cubic centimeters or liters.
It's called the specific gravity of a material, and it is the weight of a specific volume of material, compared to an equal volume of water, expressed as a number. Galena, for instance, has a specific gravity of 7.4, indicating that it is 7.4 times heavier than water.
Fill a beaker with water, and weigh it. Weigh a sample of the mineral. That's the mass of the mineral. Put the sample in the beaker and weigh that. The weight of the water-filled beaker plus the weight of the mineral sample will be greater than the weight of the beaker with mineral sample and water. The difference is the weight of the displaced water, in grams. The volume of the mineral sample, in cubic centimeters is equal to the weight of the displaced water, in grams. Calculate the specific gravity of the mineral by dividing the weight of the mineral sample by the volume of the mineral sample. Example: your beaker weighs 40 grams. Filled with water, it's 1040 grams. The sample of mineral weighs 160 grams. The beaker with the sample of mineral and water weighs 1179.7 grams. The mineral, and the beaker with water would have a combined weight of 1200 grams, but the beaker with mineral and water weighs 20.3 grams less than that, so the mineral sample is displacing 20.3 cubic centimeters of water. Given a mass of 160 grams and a volume of 2.03 CC, the specific gravity would be found by dividing 160 by 20.3. It's 7.85. (Which happens to be the specific gravity of some iron.)
Milligram is a weight and cannot be compared to a liquid volume.
weight = mass * gravitational constant. Newtons (weight) = kg * m / sec^2 for instance.
The Buoancy Method.
CC is unit of volume and lb is unit of weight. These two cannot be compared.