Geology
Specific Gravity Lab
Name____________________
One method of identifying minerals is to determine specific gravity. The specific gravity of a substance is a
comparison of its weight in air to its weight in water. An object will weigh less in air than it will weigh submerged
in water (or any fluid, for that matter). This is according to Archimedes’ Principle which states, any object
submerged in a fluid will be buoyed up by a force equal to the weight of the displaced fluid. A physics proof will
show that the specific gravity of a substance is also the same number as its density when measured in g/mL.
Suffice it to say that specific gravity is the same number as density, but is a number with no units. The reason
there is no units is that specific gravity is a pure number indicating how many times more dense (or more heavy for
equal amounts) something is than water. Water has been “assigned” a density of 1 g/mL (since the metric system
was based on the measurements for water the density works out to be 1 g/mL…….a 1 cm3 little block containing
water has a mass of 1 g). Pure aluminum has a density of 2.7 g/mL and a specific gravity of 2.7……..it is 2.7 times
heavier than the same amount of water.
To find specific gravity in this lab you will need to mass the mineral in air and then mass it in water. Plugging these
values into the following formula will give the specific gravity of the mineral. One should only determine the
specific gravity of pure mineral samples
SG = (weight in air)/(weight in air – weight in water)
Data and Calculation Table:
Mineral
mass in air (g)
galena
quartz
pyrite
orthoclase
augite
fluorite
corundum
calcite
mass in water (g)
specific gravity
Book value of SG
Questions:
1. What is the relationship between SG and density, other than they are the same number?
2. Rank the minerals listed above from smallest to largest specific gravity (Book values).
3. Anything less than 3.0 is low SG, between 3.0 and 4.5 is medium SG, and higher than 4.5 is high SG. Classify the
above list as low medium or high SG.
Galena - __________ quartz - ____________ pyrite - ____________ orthoclase - ___________
Augite - __________ fluorite - ___________ corundum - ____________ calcite - ____________
4. Shake each of the minerals you tested, back and forth. Literally get a feel for SG (low, medium or high). Next
take the unknown samples #1 through #5, shake them and classify them as low, medium or high SG. Fill in the
chart.
#1 - ____________ #2 - ___________ #3 - ___________ #4 - ____________ #5 - ____________