Heather has taught high school and college science courses, and has a master's degree in geography-climatology.
Definition of Basalt
With a name derived from the Latin for 'very hard stone', basalt is indeed a very hard, black igneous rock found all over Earth and our solar system. It can be found not only on Earth, but also on Earth's moon and Mars. It is an extrusive igneous rock, which forms from volcanic lava that cools rapidly at Earth's surface. It is generally black in color due to the high amounts of magnesium oxide and calcium oxide, and very low amounts of lighter colored silicate minerals. It has several industrial applications, including building materials and thermal insulators.
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- 0:02 Definition of Basalt
- 0:41 Chemistry of Basalt
- 1:37 Formation of Basalt
- 2:28 Uses for Basalt
- 3:03 Basalt on Other Planets
- 4:03 Lesson Summary
Chemistry of Basalt
Basalts are composed primarily of magnesium oxide (MgO) and calcium oxide (CaO). They are very low in silicon (SiO2), usually less than 50 percent. They also contain some iron oxide (FeO) and aluminum oxide (Al2O3). As a result, they are very dark in color, and usually appear as shades of black and black-green. Occasionally, some red or orange colors can appear in basalts and are due to that particular basalt containing rusting iron compounds. Basalt is an igneous rock that forms from the cooling and crystallization of magma. And usually, magma is formed from the melting of dark colored peridotite and pyroxene-rich rocks. There are some lighter colored basalts found, which form when a basalt magma contains a higher than normal amount of calcium or sodium minerals.
Formation of Basalt
Basalt is an extrusive igneous rock. All igneous rocks form as the result of the cooling and crystallization of magmas, either at Earth's surface or below the surface. If the rock hardens below the surface, it forms large crystals and is referred to as intrusive. If it hardens at the surface, it forms small crystals (because it doesn't have sufficient time for crystals to grow in size) and is called an extrusive rock. Basalt forms at the surface and has small crystal grains, and is, therefore, an extrusive rock. When basalts form at the surface, it does not have to be on a dry surface, as many basalts form in the water. Pillow basalts form when basalt lavas erupt into ocean waters, and basalt is also formed at the earth's mid-ocean ridges (where new ocean crust is formed).
Uses for Basalt
While it isn't as widely used as limestone or granite, basalt does have some uses. It can be used for structural building materials, like bricks or foundations, and sculptures. Certain shapes of basalt can be used for cobblestones and exterior road or landscape materials. And when it is heated and processed in a certain way, it can produce a product known as stone wool, which is used as a thermal insulating product. Samples of basalt from the moon and Mars are most frequently seen as museum samples or in high-end personal rock collections.
Basalt on Other Planets
Have you ever looked at the moon on a clear night and noticed darker areas on its surface? Those dark areas are actually ancient basalt lava flows on the moon's surface. Many of these rocks were collected during the Apollo (American) and Luna (Russian) space programs during the 1960s and 1970s. Chemically, Earth-based and moon-based basalts tend to differ in their metal content. Lunar basalts tend to have much higher iron contents than Earth's basalts do, and also more titanium. Despite having higher metal contents, lunar basalts tend to have little to no rust (oxidation) on them, likely due to the lack of oxygen they have been exposed to in their lifetimes. They also lack any water content, while many of the earth's basalts erupt in or near water. Recent missions to Mars have also collected samples that provided evidence of basalt rocks on Mars, although we don't know nearly as much about Martian basalts as we do the moon's basalts.
Let's review. Basalt is a typically dark-colored, extrusive igneous rock, and igneous means that it formed from rapidly-cooled lava on the earth's surface. Remember that extrusive means it hardens at the surface; it forms small crystals. And inturisve means it hardens below the surface; it forms large crystals.
It has small crystal grains because it cools rapidly at Earth's surface once it is erupted from a volcano or mid-ocean ridge. It contains more calcium and magnesium than silicon, leading to its dark color, which can range from black to green to rust red. It is common worldwide and can be found both on land and in oceans, and also on the moon and Mars. It has some uses in the building and landscape industries and as an industrial insulator material.
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What is Basalt? - Definition, Uses & Composition
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