Images

A drill core from near Waco, Texas. This core was drilled by USGS during field work for an oil and gas assessment for the Eagle Ford of the Gulf Coast Basins. Cores like these provide information on the various rock layers, such as their make-up, their age, etc.

A drill core from near Waco, Texas. This core was drilled by USGS during field work for an oil and gas assessment for the Eagle Ford of the Gulf Coast Basins. Cores like these provide information on the various rock layers, such as their make-up, their age, etc.

A drill core from near Waco, Texas. This core was drilled by USGS during field work for an oil and gas assessment for the Eagle Ford of the Gulf Coast Basins. Cores like these provide information on the various rock layers, such as their make-up, their age, etc.

Helicopter arriving to pick up geologists after retrieving geophysical equipment from the flanks of Redoubt Volcano, Alaska, July 2015

USGS researchers collecting a soil sample for rare earth elements at the Roy Creek prospect, Alaska. Jamey Jones is holding the bag while Erin Todd shovels soil into the bag.

Preliminary map of selected minerals for a portion of the Nabesna area of interest, near Orange Hill and Bond Creek deposits in Alaska. The image, derived from HyMap imaging spectrometer data collected in July 2014, is draped on shaded relief.

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

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 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.

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.

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

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.

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.

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.

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

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.