Rockhunters look for rocks at the beach, in the mountains, wherever they are.
No matter where you go on earth, you will find rocks of one variety or another just waiting for a young rockhound to come collecting. But once you have your specimens, the challenge is to figure out what kinds of rocks you have. Rocks have several characteristics used for classification. With a field guide and a few basic tests, you can learn to identify rocks like a geologist and teach other kids about the life story of your rock.
Instructions
1. Inspect the rock for signs that it is igneous, metamorphic or sedimentary. Igneous rock is often dark colored and heavy, with two sizes of visible grains and lots of holes formed by the volcanic gasses from which it came. A fossil is a sure sign of a sedimentary rock. They also tend to be lighter in weight and color than the igneous, and their grains are tightly packed. Metamorphic rocks have a large grain texture, visible layers alternating light and dark colors. Once you have deduced the rock type, you can narrow your search to those listed in the corresponding section of the field guide.
2. Scratch your rock sample in turn with a finger nail, a copper penny, a pocket knife or common nail, a piece of glass, a steel file or concrete nail in turn until something makes a mark allowing you to estimate its mineral hardness according to the Mohs scale. Alternately, you can collect a sample of each of the rocks listed on the scale and try to scratch each rock with these samples for a more accurate estimate of where it falls on the hardness scale.
3. Look at the color of the rock and match it with the correct color family in your rock guide. Scrape it across an unglazed white porcelain tile and observe the streak color for another factor to match with the guide's description of rock characteristics.
4. Hold your rock up to the light to determine whether it is transparent, translucent or opaque. You will be able to see through a transparent rock whereas light passes through a translucent rock but nothing is visible when you look through it. Opaque rocks do not let any light through.
5. Observe the luster of the rock: metallic or nonmetallic. All metals are, of course, metallic. The non-metallic rocks are classified as glassy, brilliant, resinous, greasy or waxy, pearly, silky or dull.
6. Hit your rock sample with a hammer and watch to see whether it shatters, flattens or breaks along the planes of weakness. The shape of the cleavage may be cubic, rhombohedral, or basal and will be cleanly and evenly divided. A fracture, on the other hand is jagged and uneven. Fracture classifications are conchoidal, fibrous or splintery, hackly, uneven or irregular. If you have carefully narrowed your search with each rock characteristic, you should at this point be able to pinpoint which type of rock you have.
Tags: your rock, each rock, field guide, match with, rock sample
