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.

Are all rocks fluorescent and how can I see the glow at home?

This week's question comes up many times at rock collecting shows and was asked this week.  Are all rocks fluorescent and how can I see them glow at home?

All minerals have the ability to reflect light. That is what makes them visible to the human eye. Most minerals however, do not fluoresce.  Only about 15% of minerals have an interesting physical property known as "fluorescence". These minerals have the ability to temporarily absorb a small amount of light and an instant later release a small amount of light of a different wavelength. This change in wavelength causes a temporary color change of the mineral in the eye of a human observer.

The color change of fluorescent minerals is most spectacular when they are illuminated in darkness by ultraviolet light (which is not visible to humans) and they release visible light. The photograph above is an example of this phenomenon.

Fluorescence in minerals occurs when a specimen is illuminated with specific wavelengths of light. Ultraviolet light, x-rays and cathode rays are the typical types of light that trigger fluorescence. These types of light have the ability to excite susceptible electrons within the atomic structure of the mineral. These excited electrons temporarily jump up to a higher orbital within the mineral's atomic structure. When those electrons fall back down to their original orbital a small amount of energy is released in the form of light. This release of light is known as fluorescence. 

In order to see this spectacular vision at home, we have home based ultraviolet lamps.   These come in different wavelengths which are needed for certain specimens.  There are 3 wavelengths known to cause this fluorescence: Shortwave (254nm), Midwave (315nm) and Longwave (400nm). Longwave UV is very close to what you have possibly seen in stores as a "black light", and is the least expensive method. 

The vast majority of fluorescent minerals fluoresce under Shortwave UV Lamps.  We carry both battery operated and plug-in models of these types of UV lamps.  Scientists actually utilize these lamps to help them identify specimens.  Ideally, you can also get these types of Ultraviolet Lamps with Filters placed on them to filter out more visible light.  However, these filters are very expensive.  To get at least some home enjoyment out of your fluorescent rocks, we suggest picking up one of our Ultraviolet Lamps so you can see for yourself what types you have!

To stand or not to stand, that is the question of mineral stands...

Displaying our rocks & minerals can be quite an adventure, and also complicated.  After countless hours of hunting for rocks & minerals, whether at a quarry or a rock show, they deserve a special place in your home displayed in all their glory.  After all that effort, they certainly don't belong under your bed, in a closet, locked away in a box where you can't see their natural beauty.

One can either place them on a coffee table, a bookshelf, a curio cabinet, or a display case.  Scatter them all over your home, using rocks with different colors and features to complement your home.  But no matter which option you choose, you need to choose the right mineral stand to complement and support the rock and insure its safety.

There are many types of mineral stands for a reason.  Each rock has a unique shape and size, and of course color.  There are triangle mineral stands shown at right.  There are peg stands shown at left.  And there are even mineral stands carved out of wood shown at right below.

These are just a few of the many mineral stand options for you to choose and there is no single right mineral stand for a particular species.  Try one that you think fits your rocks.  More than likely it will work for you, but if it doesn't chances are you probably have another mineral in your collection that it will work on.  Spend a few dollars and get your favorite minerals out of the closet and up on display on a mineral stand. 

Organizing and Displaying Your Rock Collection

This week's post is about how to easily organize and display a rock collection that I found posted somewhere which I have paraphrased for the benefit of our readers:

1.  Identification - Once you have a rock specimen, you need to identify it.  There are hundreds of different rock types that can be identified, but all rocks can be grouped into one of three basic types of rocks,  Igneous, Sedimentary, and Metamorphic. 
2. Labeling - Now that you have identified your rock type, label it.  Write down on an index card the rock’s common name if you know it, the type of rock it is, where it was found and the date it was collected.  By labeling your rocks, you can now organize them into groups which can then be stored together or displayed.
3. Cataloging - Cataloging is an extension of the labeling process.  A catalog is a documented archive of your rock collection.  Each rock specimen has its own label which identifies it.  Your catalog keeps a record of all your rocks.  As your rock collection grows, your catalog will also include information on where your rocks are stored.  This can be done on paper or in a simple spreadsheet on your computer.
4. Display - The last step to organizing your collection is to decide how you will display and store your rocks.  By displaying your rocks both you and others can appreciate their natural beauty.  When displaying your rocks be sure to keep the rock specimen and label together.  Using a protective container is an especially good idea for fragile samples.  Acid free tissue papers can be used to protect especially fragile specimens.  We have a wide variety of Rock Display Cases, Easels and Stands to make your collection look exactly how you want it to look.