Ship Rock in northwest New Mexico

Ship Rock (also spelled, incorrectly, by some authors as "Shiprock") is an erosional remnant (plug) of the throat of an explosive volcanic eruption, which occurred 27 million years ago during the late Oligocene.

Ground view of Ship Rock, which stands approximately 500 m above the surrounding land. The two main wall-like dikes can also be seen in this view.

The peak elevation of Ship Rock is 7,178 feet (2,188 m) above sea level. The main part of the landform rises 1,583 feet (483 m) above the surrounding high desert in northwest New Mexico, a few miles southwest of the town of Shiprock (one word), New Mexico.

All the following images are via Google Earth (2018).

Overview satellite image

Medium-closeup image.

The landform consists of fractured volcanic tuff breccia with subsidiary minette (lamprophyre) dikes. In addition, several wall-like sheets radiate (various distances) away from the central formation. Ship rock is a classic example of a diatreme volcano, or one that formed explosively from gas-charged magma escaping at great velocity.

Very closeup image. Scale is 1 mile.

Ship Rock is one of more than 80 Oligocene to Miocene (about 28 to 19 million years old) volcanoes and intrusive features in the Four Corners (Utah, Colorado, New Mexico, and Arizona) region of the Colorado Plateau.

For a concise, yet detailed summary on the geology of this iconic landform, Google the phrase: "black rocks protruding up." You will be able to obtain a free pdf by Semken (2003).

The landform is sacred to the Navajo and is located on the Navajo Indian Reservation, which is private property.   

Andalusite, a mineral with an unusual feature

Andalusite is a metamorphic rock mineral (aluminum-neosilicate mineral = Al2Si05). Because its formation involves contact metamorphism (i.e., heating of rocks near the intrusion of igneous magma), andalusite is resistant to high heat and can be used in making spark plugs, furnaces, and kilns.

Cross-section of a crystal of andalusite (variety chiastolite);
 33 mm width.

The variety chiastolite contains dark inclusions of graphite (carbon), which form a very distinctive and sharply delineated cruciform pattern, when shown in cross section. The graphite is pushed aside by crystal growth during metamorphism. Specimens can be of gemstone quality. Chiastolite is also used to make amulets and charms.

Oblique view of same specimen as above; 30 mm height.

Notice how the black band of graphite on the side of the crystal is coincident with one of the rays of the cruciform pattern. Each  of the rays is coincident with a black band. This crystal occurs in a mica schist, which is the most common occurrence of andalusite.