How to Identify Basalt

Gabbro has the same composition as basalt.
••• Hemera Technologies/Photos.com/Getty Images

Basalt, a volcanic igneous rock, occurs worldwide, but especially in India, Scotland, Greenland, Iceland, Canada and the northwestern United States. Most basalt occurs as lava flows, in narrow dykes or sills. It's the basalt from lava flows that make up the enormous sheets of a lava plateau. This rock is easy to identify.

    Note the rock's color. Basalt appears black or grayish-black, sometimes with a greenish or reddish crust.

    Feel its texture. Basalt consists of a fine and even-grain. The dense rock has no crystals or minerals discernible to the naked eye. When freshly broken, basalt has a dull surface.

    Determine its structure with your naked eye or a microscope. Often vesicular or amygdaloidal, basalt has columnar jointing.

    Examine your rock's composition with a microscope. Basalt occurs more often as pyroxene (shiny, black) and as plagioclase (tabular, white-gray). The presence of olivine gives basalt a green, glassy appearance and is called olivine basalt. Also present may be iron ore (ilmenite and/or magnetite) or bronze-colored biottie.

    Tips

    • Varieties of basalt include olivine basalt and quartz basalt, which contains a minuscule amount of quartz. Basalt is used as a source of iron ore, roadstone aggregate, sapphires or native copper.

Related Articles

Interesting Facts About Quartzite
How to Identify Sandstone
How to Recognize Rough Agate
How to Identify Unpolished Agates
What Is Drusy Quartz?
List of Rare Minerals
List of Igneous Rocks That Do Not Contain Quartz
How to Identify Rough Gem Stones
How Can I Tell the Difference Between Fluorite & Quartz?
How to Do a Streak Test With Rocks
List of the Minerals Found in the State of Washington
How to Tell the Difference Between Talc & Gypsum
The Characteristics of Slate
Where Is the Mineral Topaz Found?
The Differences Between Fluorite & Calcite
Physical Properties of Calcite & Quartz
How to Identify Obsidian
How to Identify Valuable Rocks
How to Tell if a Rock Is a Meteorite?
How Is Rose Quartz Formed?