Texas Rocks!

Yes it does, and they are found everywhere you look. Do you like collecting rocks? Have you noticed that rocks are different from one place to another? The rocks that you pick up and add to your collection used to be part of much bigger rocks. In fact, the whole planet earth is made of rock, even under the ocean! Scientists who study rocks are called Geologists. There are three classifications of rocks: igneous, sedimentary and metamorphic.

Igneous:: These are rocks that were formed from melted rock that has cooled and solidified. Many of these rocks are very smooth and fine-grained like quartz, granite and obsidian (volcanic glass).
Sedimentary:: These rocks are formed on the surface of the earth, either on land or water. They are created by the accumulation of layers of sediment and small bits of other rocks, sand, animal and plant material. Most sedimentary rocks are cemented together by minerals or chemicals or by electrical attraction. Some are loose. The layers are usually parallel or nearly parallel to the earths surface, unless there has been geologic movement of the rock since it was deposited. Fossils are found in some sedimentary rocks.
Metamorphic:: These rocks are formed deep in the earth when igneous or sedimentary rocks come under enormous pressure or heat. They are not melted, rather they are compressed into denser rocks. The minerals are changed by the compression or by liquids which are introduced into the process. Granite gneiss and biotite schist are two types of metamorphic rock which appear to be striped.

Starting Your Collection

A good rock collection consists of selected, representative, properly labeled specimens. The collection can be as large or as small as you like. As your collection grows, you can replace poor specimens with better ones. The best place to start your collection is your own neighborhood. You might not see a lot of variety, but it will accustom you to looking at rocks critically.

Identifying Rocks

Get yourself a rock and mineral guide - there are lots to choose from, and you can even get them at used book stores for a bargain. Geologic maps are helpful too. They show the distribution and extent of particular rock types or groups of rock types. Depending on size and scale, the maps may cover large or small areas. Most have brief descriptions of the rock types. Some are issued as separate publications; others are included in books.

Order Bureau of Economic Geology Maps

Where to Find Rocks

The best collecting sites are quarries, road cuts or natural cliffs, and outcrops. Open fields and level country are poor places to find rock exposures. Hills and steep slopes are better sites. Almost any exposure of rock provides some collection opportunities, but fresh, unweathered outcrops or manmade excavations offer the best locations. If possible, visit several exposures of the same rock to be sure a representative sample is selected.

Collecting Equipment

Two pieces of equipment are essential for the beginning rockhound: a geologists hammer (rock hammer) and a hand lens or loop. The hammer is used to break off fresh rock specimens and to trim them to display size. It can be purchased through hardware stores or scientific supply houses. The head of a geologist's hammer has one blunt hammering end. The other end of the most versatile and widely used style is a pick. Another popular style-the chisel type-has one chisel end; it is used mostly in soft sedimentary rocks and in collecting fossils.
The hand lens, sometimes called a pocket magnifier, is used to identify mineral grains. Hand lenses can be purchased in jewelry stores, optical shops, or scientific supply houses. Six-power to ten-power magnification is best.

Other pieces of necessary equipment are inexpensive and easy to find: a knapsack to carry specimens, equipment, and food; bags and paper in which to wrap individual specimens; a notebook for keeping field notes until more permanent records can be made; and a pocket knife to test the hardness of mineral grains.

Hints for Rock Collectors

Label specimens as they are collected. Identification can wait until later, but the place where the rocks were found should be recorded at once.
Trim rocks in the collection to a common size. Specimens about 3 by 4 by 2 inches are large enough to show rock features well. Other display sizes are 2 by 3 by 1 inch, or 3 by 3 by 2 inches.
Ask for permission to collect rocks on private property. The owners will appreciate this courtesy on your part.
Be careful when collecting rocks. Work with another person, if possible, and carry a first aid kit.
Wear protective clothing--safety glasses, hard-toed shoes, hard hat, and gloves--when dislodging specimens.
Avoid overhanging rock and the edges of steep, natural or quarried walls.
Do not collect rocks in national parks and monuments or in State parks; it is illegal. Similar rocks commonly crop out on land nearby.
Please do not collect anything in any cave, no matter if it is on public or private property. Caves are habitats for many animals and invertebrates and these ecosystems exist in a delicate balance. Any disturbance could cause permanent damage.
Join a mineral club or subscribe to a mineral magazine. They occasionally discuss rocks.
Collecting rocks from each State or country has no scientific significance. The distribution of rocks is a natural phenomenon and is not related to political divisions.

Selected by the SciLinks program, a service of National Science
Teachers Association. Copyright 1999 - 2002.

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