How do I find 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 scale, ultraviolet 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

Testing

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 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 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 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

Before you buy a magnifier...

After you buy your rock hammer and map out what geological place you will want to explore, make sure to pack your rock magnifier loupe or jewelers loupe.  You will want a lightweight, powerful magnifier loupe that has impeccable optics and is easy to use. Get the best magnifier for demanding jobs like inspecting gems; in the field, for quick looks at minerals, buy a decent magnifier you can afford to lose...

How to Use a Magnifier

Hold the loupe up next to your eye, then bring your specimen close to it, only an inch from your face. The point is to focus your attention through the lens, the same way you look through eyeglasses. If you normally wear glasses, you may want to keep them on.  A magnifier won't correct for astigmatism.

How Many X (Power)?

The X factor of a magnifier refers to how much it magnifies.  Geologists (and Numismatists) like to have 5x to 10x, but more than that is hard to use in the field because the lenses are very small. 5x or 7x lenses offer a wider field of vision, while a 10x magnifier gives you the closest look at tiny crystals, trace minerals, grain surfaces, and microfossils.   Most people find that a 10x loupe is just the right level of magnification to provide the best magnification, light capture, and depth of field.  Given the same X factor, a larger lens of course is better.  So is a ring or loop to attach a lanyard, as well as a leather or plastic case to keep the dust off.

Magnifier Flaws to Watch For

Check the lens for scratches. Set the magnifier loupe on a piece of white paper and see if the lens adds color of its own. Now pick it up and examine several objects, including one with a fine pattern like a halftone picture. The view through the lens should be clear as air with no internal reflections. Highlights should be crisp and brilliant, with no colored fringes (that is, the lens should be achromatic). A flat object should not look warped or buckled— move it around to be sure.  Good lensmakers combine three pieces of glass to correct for chromatic aberration— what gives an image blurred, colored fringes. Doublets (two pieces can be satisfactory, but the triplet is the gold standard.

 

Triplets are made of three (3) lenses. Every lens refracts (bends) the light passing through the glass. Different wavelengths (color) of light is bent a different amount. The combination of the 3 lenses bonded together to form one lens are engineered so that the light coming into the lens is corrected so that the light coming out of the lens is color correct, or the lens is achromatic correct. The triplet lens is also aplanatic meaning that the lens is corrected for spherical aberration making the image clear and in focus from the center to the edges.

 

Folding magnifiers, magnifiers made of of multiple lenses that fold in and out of a housing are handy for providing simple magnification at multiple levels but each lens and the air gap between each lens refracts the wavelengths a different amount. The image is distorted across the lens and the color you see are not the same as those of the object you're viewing.

Many of the cheap loupes available on the market are simply made of multiple magnifying lenses stacked on top of each other in a metal barrel. The result is gross image and color distortion, but at a very cheap price.