Images

This sample is of bituminous coal, a middle rank coal (between subbituminous and anthracite) formed by additional pressure and heat on lignite.

Clinker coal is the result of a seam of coal catching fire and burning so hot that it baked surrounding rock layers into brick-like formations.

A sample of lignite, the lowest rank of coal. It is primarily mined for burning in steam-generation power plants.

Peat is the precursor to coal. It's made up of decayed plant materials or other organic matter that, over time, can undergo heat and pressure to become lignite.

This sample is of peacock coal. Peacock coal is not a specific class of coal, but rather the name for an effect in which oxidizing materials in the coal create a dazzling array of colors on the surface of the coal. Usually it is short-lived, as the material fully oxidizes away shortly after exposed to air.

This is anthracite, the highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter. Anthracite is not as commonly mined as other ranks of coal.

Clinker coal is the result of a seam of coal catching fire and burning so hot that it baked surrounding rock layers into brick-like formations. Some of the most famous clinker formations in the United States can be seen at the Theodore Roosevel National Park in North Dakota.

Cannel coal is a type of bituminous coal that is also sometimes referred to as a type of oil shale. It's name likely came from the word "candle." Cannel coal was once used as a source for kerosene.

Clinker coal is the result of a seam of coal catching fire and burning so hot that it baked surrounding rock layers into brick-like formations.

A sample of lignite, the lowest rank of coal. It is primarily mined for burning in steam-generation power plants.

A sample of lignite, the lowest rank of coal. It is primarily mined for burning in steam-generation power plants.

Most fossils occur in sedimentary rocks including shale, limestone and sandstone. The sandstone block shown here contains a large fossil palm leaf, found at the Coryell Coal mines in Colorado.

Faulted and folded Triassic, Jurassic, and Cretaceous rocks along Surprise Creek in southern part of Western North Slope. The Triassic and Jurassic rocks include petroleum source rocks from which oil was generated. Geologists in orange vests for scale.

Geologist describes petroleum source rocks in Triassic and Jurassic rocks along Surprise Creek in southern part of Western North Slope.

Geologists measuring petroleum source rocks in Triassic rocks along Surprise Creek in southern part of Western North Slope.

A field assistant pans for monazite and rare earth minerals in Wolf Creek, which cuts through the Melozitna granite. This area is part of the Bureau of Land Management's Central Yukon Planning Area, where USGS did a critical mineral assessment in 2015.

Productive tallgrass prairie with potential for growing biofuel crops.

A drill rig on a drill pad in Karnes County, Texas.

A carbon dioxide (CO₂) injection well drilled by the Southeast Regional Carbon Sequestration Partnership (sponsored by the U.S. Department of Energy) at the Cranfield CO₂ test site in Mississippi. The well was drilled to test the effectiveness of injecting and storing CO₂ in a deep saline reservoir.

A geothermal power plant at The Geysers near Santa Rosa, California. The USGS researches and assesses geothermal resources.

USGS researchers used a small-scale commercial windmill as an essential part of its new device to measure snowfall in remote areas.