Page 5--Rocks and Minerals


Rocks are one of the main sources of information for geologists. By comparing rocks and minerals and their locations, geologists can estimate approximately how old the rocks and minerals are. They can tell if a rock was formed on dry land, on an ocean floor, or deep inside the earth.

Other people besides geologists have found rocks and minerals useful. The Indians used native stone to make tools, weapons, and pottery. Early settlers constructed buildings, bridges, and fences out of limestone and sandstone. Indians and settlers used natural caves for protection and rock outcrops for lookouts; and they carved pictures, called petroglyphs, in the rock walls.

Figure 8. Ancient carvings on rock exposures are called petroglyphs. This one was carved in sandstone by Indians in Ellsworth County in central Kansas.

Kansas also has had its share of fortune hunters. More than once people have traveled through the state seeking valuable minerals such as gold and silver.

In 1541 the Spanish explorer Francisco Vazquez de Coronado was told of an Indian land named Quivira where gold and other riches were abundant. His desire to find Quivira led him into a territory that is now part of Kansas. But Coronado and his men went away disappointed. They never located gold, which apparently existed only in Indian legends.

More than 300 years later in the 1880's, hundreds of prospectors flocked to Logan County in western Kansas hoping to find silver. Thousands of dollars were spent to stake claims, but only traces of nickel ore were found. Scientists who visited the area didn't think conditions were right for either silver or nickel to form. The traces of the minerals were probably found in rocks from outer space, called meteorites, which had collided with Earth.

Although not much gold or silver has been found in Kansas, coal, gypsum, lead, zinc, chalk, salt, volcanic ash, limestone, sandstone, clay, sand, oil, and gas have all been found and used to make various products. Because of their many uses, rocks, minerals, and other natural resources add to the wealth of Kansas. They bring money and jobs. They also add to the environmental wealth. Undisturbed rocks and minerals add color, form, and beauty to the landscape.

Figure 9. Oil and gas were first discovered in Kansas in the 1860's. Wells, such as this oil well in Comanche County in southwest Kansas, are now located throughout the state.

We know that rocks and minerals are all around us, but what are they?

Minerals

Minerals occur naturally in the Earth. They are not made by people. They also are inorganic. This means they are not made from living material; no part of a mineral was ever alive.

All minerals are made of smaller units called elements. A few minerals, such as gold and silver, are made of only one element. These minerals are called native elements. Sulfur is the only native element found in Kansas. All other minerals are a combination of two or more elements.

Minerals can be identified by their color and hardness. The scale for hardness ranges from 1 to 10; the harder a mineral is, the higher its number. A diamond, which is very hard, rates a 10. Garnet is one of the hardest rocks found in Kansas. It is a 7 and is so hard it can scratch window glass.

Pyrolusite, another Kansas mineral, is at the lower end of the hardness scale. It is a 1 or 2 on the scale and is soft enough to leave a black streak when rubbed on a piece of paper.

Galena, sphalerite, pyrite (fool's gold), halite (salt), calcite, anhydrite, gypsum, mica, and quartz also are found in Kansas. Many other minerals occur in the state, but none in large quantities.

Rocks

A rock is usually made of one or more minerals. Most rocks we see on the Earth's surface have been broken up into small pieces. Sand, gravel, clay, and silt are all made of particles worn from rocks.

Rocks that are buried are called subsurface rocks because they are located below the Earth's surface. Subsurface rocks are often found in large slabs called beds. Beds are sometimes seen at the surface, but often in Kansas they are covered by soil. They can be several feet thick, extend for many miles, and be layered one on top of another. Unless the beds are disturbed by forces such as earthquakes or volcanoes, the deeper beds are usually older than the ones closer to the surface.

Figure 12. Layers of sedimentary rocks often form in flat beds. Sediment deposited on the Earth's surface compresses earlier deposits into hard rock. When beds are formed in this way, the deepest ones are the oldest.

Figure 13. Sometimes wind and water carve hills and valleys into the surface that are later buried. Magma also may force its way up from deep inside the Earth. When magma cools, a solid rock is formed within the layers of rock already there. This type of formation is called an intrusion (A). Rocks inside the earth may break and shift along a fault (B). These shifts, if big enough, may cause earthquakes.

Sometimes rocks that were once underground are exposed by erosion. These exposures are called outcrops. In some places, the hills have been cut away to make roads more level. Areas cut away for roads are called roadcuts.

Figure 14. Underground rock beds, formed over millions of years, were exposed when part of a hill was cut away for a road.

Rocks are organized into three categories depending on the way they are formed. These categories are sedimentary, igneous, and metamorphic.


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Kansas Geological Survey
Placed online Feb. 1, 1996
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