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Basics for Beginners: Reference books and identifying minerals
LEARNING ABOUT MINERALS can be a lifelong task. The best way to start out is by getting to know someone else in the hobby. Get them to show you some different minerals and tell you the differences between them. There are over 900 rock and mineral clubs in the United States, and all of them welcome new members. Here is a link to the national list of rock clubs. Certainly one will be close to you! The Hot Springs Geology Club in central Arkansas gives free memberships to students. Ask about student discounts at a rock club near you.
Build your library*
The next best way to learn is from the books you can get in your local bookstore or order from an online bookstore. We recommend these inexpensive paperbacks:
Rocks and Minerals - Golden Nature Guide by Zim and Shaffer
A field guide to Rocks and Minerals. (Peterson's Field Guide) by Frederick H. Pough
Simon and Schusters Guide to Rocks and Minerals
**See our reviews of these books at the bottom of this page**
If you are just beginning rock collecting, this page will introduce you to some of the language of rocks and minerals. Some of the words may look big, but they are useful because they describe a property, or something special, about that rock or mineral. The larger your vocabulary of these words, the better you will be able to understand rocks and minerals.
Just what is the difference between a rock and a mineral?
Let's define a mineral and a rock, noting the differences between the two.
A mineral is a natural substance which has its own distinctive structure and may have its composition expressed with a chemical formula. Some examples are quartz, calcite, and galena. Quartz has the chemical composition Si02.
A rock is usually composed of 2 or more minerals in some physical combination, although some rocks are composed of only one mineral. Examples of rocks are limestone, sandstone, granite, or shale.
(If you wanted to think of a comparison to food, a mineral would be like flour and sugar, and a rock would be a cake.)
About 100 minerals are relatively common. There have been over 4000 minerals identified by mineralogists, but only about the hundred or so are easily collectable. Some collectors want to obtain a piece of every known species, but this is impossible because some are so rare.
Properties of minerals
You can tell the differences between minerals by looking for certain properties. Because each mineral is unique both chemically and structurally, each has its own set of physical, optical, and structural properties which aid in its identification.
Chemistry refers to the basic building blocks that the mineral is made of. Optical properties are the way a mineral looks and what light does when it shines on it. Physical properties such as hardness and streak can be tested easily. Most geologists only do the most basic physical property tests for an identification, so we will briefly discuss some physical properties.
Physical properties
Let's consider the physical properties that are easy to test. They may be divided into 2 groups: those concerned with the effects of light on the mineral, and other tests.
Light-dependent properties: The easiest tests to do are about how light interacts with the mineral. These are color, luster and diaphany. You can do all of these light tests using only your eye.
Color is the most obvious property of the mineral , but it is also the least usable because a given mineral, like quartz, may have a variety of colors (colorless, purple, blue, pink, black, violet, green, tan, et cetera).
Luster is easy to tell by looking at the mineral. Does the mineral reflect light like a piece of metal? If so, then it has metallic luster. If not, then it has non-metallic luster. Non-metallic luster is further subdivided into how brilliant the mineral reflects the light: vitreous (like glass), adamantine (brilliant, bright like metal), pearly, greasy, oily, dull, et cetera.
Diaphany means how translucent the mineral is. Can you see through it like a clear crystal, or not? Or maybe just a little. The answers for diaphany may be opaque, translucent, or transparent. This property is usually noted for a thin chip of the mineral because if the mineral is strongly colored, it may mask this property.
Other Properties of Minerals
Specific gravity is the measure of each mineral's own unique density and how it compares to the density of water. The mineral's density is what makes the mineral heavy or light. Some minerals are very dense, like the native metals copper, silver, or gold, and some are even lighter than water and will float! Volcanic pumice will float on water. You have to have a specially designed balance to measure specific gravity.
Quartz is always a good mineral to compare another sample to, since it has a specific gravity of 2.54. Minerals with a specific gravity higher than around 3.2 are considered to have relatively high specific gravity. They either contain heavy atoms, like those of the middle of the Chemist's Periodic Table (titanium, manganese, iron, cobalt, nickel, copper, zinc, lead) or have a very dense packing arrangement of the atoms (like with carbon in diamond).
Streak is an easy field test to do. Interestingly, the powder of a particular mineral may or may not be the same color as the mineral! Using an unglazed piece of porcelain, like the back of a common bathroom tile, you can do a streak test. The color of the powdered mineral (the streak) may surprise you. Try it for a piece of pyrite (fool's gold).
Hardness measures how hard the mineral is relative to other minerals. It is called the scratch or hardness test. Most minerals will not scratch a quartz crystal. Many years ago, a man named Moh took a lot of minerals and tried to scratch them with each other. From his experiment, he came up with chart of the relative hardness of his minerals, one to another. This chart is called Moh's hardness scale. Talc is the softest, diamond is the hardest.
Moh's hardness scale, an easy way to remember it:
The girl could flirt and flirt quickly though Connie didn't.
Talc Gypsum Calcite Fluorite Apatite Feldspar Quartz Topaz Corundum Diamond
A chemical test allows us to determine if the mineral reacts with dilute acid. We use a drop of 10% hydrochloric acid to check for effervesence, or fizzing, and note if there is a reaction.
There are many other minor physical properties to note, such as magnetism, solubility, taste, odor, ease of melting (fusibility), and so forth. Get a basic book that discusses these properties so you can learn to do these tests yourself. Then you will not have to have an "expert" identify most of the common minerals you will find. Some books are available which present the physical properties information arranged in tables so you can use what you learn to identify the mineral yourself. One of the best of these books is an old textbook which you might pick up at a used book dealer: Mineralogy by Kraus, Hunt, and Ramsdell, 1936, McGraw-Hill Book Co. The tables are from pages 453-621, inclusive.
Location gives a really good clue as to what a mineral could be, because some minerals are well known to come from certain areas. Now that you know a little about identifying minerals, get your FIELD NOTE BOOK and MAP, and you are set to go do some collecting!
*Amazon.com is pleased to have Rockhounding Arkansas in the family of Amazon.com associates. We've agreed to ship books and provide customer service for orders we receive through special links on Rockhounding Arkansas. Prices are automatically updated on the catalog page to reflect the publisher's price, so the prices here are rough figures.
Using rock collecting tools is on the next page
Ch 12, page 2
Contact the authors of Rockhounding Arkansas revised July 2000
©Rockhounding Arkansas 1998 http://rockhoundingAR.com