What is the specific gravity of my specimen?

Divide the specimen's dry weight by the weight it loses when it hangs under water. That ratio is its specific gravity (SG), how many times heavier it is than the same volume of water [1][2]. Enter the weight in air and either the weight hanging in water or the reading on a tared cup of water, plus how finely your scale reads. The calculator returns the SG, the range your scale's rounding allows, and the common minerals whose published values fall in that range. Quartz lands near 2.65, barite near 4.5 and gold near 19 [1][2][3], so a single weighing often splits lookalikes that hardness and color cannot.

What to weigh, and in which order

The method itself has its home on measuring specific gravity at home, with photographs of the setups. The short version, from the Queensborough Community College course notes and the Maine Geological Survey activity [1][2]:

1. Weigh the specimen dry. This is A, the weight in air.
2. Get the weight of water it pushes aside, one of two ways:
   • Hanging method. Hang it on a thread from the scale so it sits fully under water, touching nothing. The reading is W, the weight in water. The calculator works out A minus W for you.
   • Cup method. Set a cup of water on the scale, tare it to zero, then lower the specimen on its thread until it is fully under water and held still. The reading is the displaced water, D, directly.
3. Enter your scale's resolution: 0.1 g, 0.01 g or 0.001 g.

Use the purest single-mineral piece you have; matrix and a second mineral pull the answer toward their own values [1]. Shake off air bubbles. Do not put halite, other salts, some borates or crumbly clays in water at all; check minerals that must not get wet first.

Why the answer comes as a range

A dense mineral loses very little weight in water, so a tenth of a gram of rounding moves the answer a long way. The calculator does not hide that. It works out the SG twice more, once as if the true weight lost were one scale step heavier and once one step lighter, and shows the span between them.

The first is the worked example on the specific gravity page; the second is an illustration, the same mineral at an eighth of the size. With the small piece, the range takes in microcline feldspar, quartz and calcite together, and SG alone cannot choose between them. That is the cue to use a finer scale, measure a larger piece, or weigh twice and average.

A worked example: is this heavy white crystal barite?

The readings here are illustrative. You have a white, tabular crystal from an old lead district that feels too heavy for calcite. You use the cup method on a scale that reads to 0.1 g.

Calcite at 2.71 and celestite at 3.95 to 3.97 are well outside the range [4], so the heft was telling the truth. Hardness would not have helped here: barite, celestite and calcite all sit in the same table of the Mineralogical Society of America's key, the one for minerals of hardness 2½ to 3 [4]. The SG did the separating. Confirm with the identification key, which takes hardness, streak and luster alongside the SG.

The reference list behind the matches

The calculator compares your range against the values used on the specific gravity page, which come from the Maine Geological Survey, the Queensborough notes and the Mineralogical Society of America's identification key. A mineral counts as a match if its published value or range falls within 0.05 of your range; that margin is the calculator's own allowance for the small differences between sources and is not a published figure.

The Queensborough notes warn that SG varies "as much as 25%" within some minerals, and that garnet and tourmaline varieties differ among themselves [1]. A result between two entries, or matching none, is common with impure or porous pieces; it is rarely a sign of an unusual mineral. Galena and cinnabar are lead and mercury minerals; if you weigh them, handle them as on handling and storing toxic minerals and pour the water away where no one will drink it.

When the number does not settle it

SG separates minerals that differ a lot in weight. It is weak between close neighbors such as quartz and calcite, where a scratch on glass does the job in seconds; those pairs are on common lookalikes. If SG, hardness and streak still disagree after careful measurement, getting a specimen tested explains what a lab can confirm and what it costs.

References

1. Queensborough Community College (CUNY), Roland Scal, Gems and Semiprecious Stones course notes, "Specific Gravity" (undated, read October 2026). https://www.qcc.cuny.edu/biologicalSciences/faculty/rscal/gems/specgrav.html
2. Maine Geological Survey, "Activity 19: The Density of Minerals," developed by Duane Leavitt (undated, read October 2026). https://www.maine.gov/dacf/mgs/education/lessons/act19.pdf
3. Mineralogical Society of America, The Mineral Identification Key, Table IIB-1: Streak not colored, cleavage prominent, hardness less than 2½ (undated, read October 2026). https://msaweb.org/msa/Collectors_Corner/id/mineral_id_keytiib1.htm
4. Mineralogical Society of America, The Mineral Identification Key, Table IIC-1: Streak not colored, cleavage prominent, hardness 2½ to 3 (undated, read October 2026). https://msaweb.org/msa/Collectors_Corner/id/mineral_id_keytiic1.htm
5. Mineralogical Society of America, The Mineral Identification Key, Table IIA: Minerals with a nonmetallic luster, definitely colored streak, and hardness 1 to 6 (undated, read October 2026). https://msaweb.org/msa/Collectors_Corner/id/mineral_id_keytiia.htm