What Is Specific Gravity?
Specific gravity (SG) is the ratio of a mineral's density to water. Quartz is 2.65, gold is 19.3, galena (lead sulfide) is 7.6. A small piece of galena feels shockingly heavy — that's SG at work.
The Water Displacement Method
Fill a graduated cylinder with water and note the level. Drop your specimen in and note the new level. The volume of water displaced (in mL) equals the volume of the specimen in cm³. Divide the specimen's dry weight (in grams) by that volume. Compare to known SG tables.
What to Look For
Very heavy for size = likely a sulfide or native metal (galena, gold, silver, wolframite). Average weight = silicates and carbonates (quartz, feldspar, calcite). Very light = evaporites or low-density minerals (halite, gypsum, borax).
Use the We Lick Rocks Weight Calculator
Our built-in mineral weight calculator lets you enter the dry weight and submerged weight of your specimen to calculate SG automatically — then cross-references it against common minerals to suggest likely identifications.