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July 19, 2014, How do I measure the specific gravity of a rock or mineral?...

July 19, 2014, How do I measure the specific gravity of a rock or mineral?...

This week I received a call from a Rock Hound asking what is the easiest way to find a minerals' specific gravity?  While we sell many rock and mineral collecting tools, like a rock scaleultraviolet lamp and other rock tools, you should have a glass beaker.  Just like the one you had in Chemistry class in high school.

First, what is specific gravity (SG) and why is it important to rock collectors?  SG is a measurement of a substance's density (degree of compactness) based on its mass concentration.  It is determined by comparing the density of the mineral specimen to the density of water.  As a control substance, water is assigned an SG of 1.

Some minerals are denser than others, so a quantity of one mineral will weigh more than an equal weight amount of another mineral which you could have tried on one of our mineral scales.

For the layman, it is done by water displacement and requires a beaker and a scale. The weight of the beaker is taken and written down, as well as the weight of the specimen. The beaker is partially filled up with water, and the level of the water is noted. The mineral is put into the beaker with water, and the water level rises. The difference in the amount of water before the specimen was put in and after it was put in is noted. The mineral is taken out, and the water is spilled out. Then the beaker is filled with the amount of water that the specimen displaced and measured. The difference in weight of the beaker when it was empty and the current measurement (the beaker with the displaced water) is the weight of the displaced water. The weight of the displaced water has the same volume as the specimen, but a different mass. The weight of the specimen is divided by the weight of the displaced water, and that number attained is the specific gravity of that specimen. - See more at: http://www.minerals.net/resource/property/specificgravity.aspx#sthash.tCH5qDhJ.dpuf

For the rock collector, density is easily calculated by water displacement and requires a beaker and a scale. as part of your rock and mineral collecting tools.  The weight of the beaker is taken and written down, as well as the weight of the specimen. The beaker is partially filled up with water, and the level of the water is noted. The mineral is put into the beaker with water, and the water level rises. The difference in the amount of water before the specimen was put in and after it was put in is noted. The mineral is taken out, and the water is spilled out. Then the beaker is filled with the amount of water that the specimen displaced and measured. The difference in weight of the beaker when it was empty and the current measurement (the beaker with the displaced water) is the weight of the displaced water. The weight of the displaced water has the same volume as the specimen, but a different mass. The weight of the specimen is divided by the weight of the displaced water, and that number attained is the specific gravity of that specimen.  Its that simple. 

Don't forget to visit our website to see our wide selection of rock collection box and display cases

For your reference, here's a List of Minerals and their Specific Gravity

 

Substance SPECIFIC GRAVITY
Amber 1.05-1.30
Lucite 1.19
Jet 1.30-1.35
Quartz 1.544-1.533
Topaz 1.62-1.64
Ivory 1.7-2.0
Opal 2.1
Obsidian 2.3-2.6
Lapis lazuli 2.4-2.9
Moonstone 2.56-2.62
Aquamarine 2.67-2.71
Emerald 2.67-2.78
Coral 2.68
Turquoise 2.6-2.8
Amethyst 2.63-2.65
Pearl 2.60-2.78
Nephrite 2.90-3.02
Glass 3.15-4.20
Peridot 3.27-3.36
Jadeite 3.35
Azurite 3.7-3.9
Diamond 3.52
Chrysoberyl 3.70-3.72
Malachite 3.75-3.95
Sapphire 3.99-4.00
Ruby 3.97-4.08
Zircon 3.90-4.71
Hematite 4.95-5.16
Pyrite 5.0-5.2
Tantalite 5.18-8.20
Gold 19.3