Clarkeite is a uranium oxide

Uranium oxide

Uranium oxide is an oxide of the element uranium.The metal uranium forms several oxides:* Uranium dioxide or uranium oxide * Uranium trioxide or uranium oxide...

 mineral of composition (Na,Ca,Pb)₂(UO₂)₂(O,OH)₃ or (Na,Ca,Pb)(UO₂)O(OH)·0-1H₂O.

The color of samples varies from dark brown to reddish orange. Clarkeite forms by oxidation and replacement of uraninite

Uraninite

Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2, but also contains UO3 and oxides of lead, thorium, and rare earth elements...

 late during pegmatite

Pegmatite

A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....

 crystallization. Although uraninite-bearing granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

 pegmatites are common, clarkeite is rare and occurs intimately intergrown with other uranium

Uranium

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 minerals.

It is known from only two localities; the Spruce Pine

Spruce Pine, North Carolina

Spruce Pine is a town in Mitchell County, North Carolina, United States. The population was 2,175 at the 2010 census.-History:Spruce Pine was founded in 1907 when the Clinchfield Railroad made its way up the North Toe River from Erwin, Tennessee...

 pegmatite district in western North Carolina

North Carolina

North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...

, USA, and Rajputana

Rajputana

Rājputāna was the pre-1949 name of the present-day Indian state of Rājasthān, the largest state of the Republic of India in terms of area. George Thomas was the first in 1800 A.D., to term this region as Rajputana...

, in the Ajmer

Ajmer

Ajmer , formerly written as Ajmere, is a city in Ajmer District in Rajasthan state in India. Ajmer has a population of around 800,000 , and is located west of the Rajasthan state capital Jaipur, 200 km from Jodhpur, 274 km from Udaipur, 439 km from Jaisalmer, and 391 km from...

 district, India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

. Clarkeite is the only known naturally occurring high-temperature uranate. The general formula for ideal clarkeite is Na[(UO₂)O(OH)](H₂O)_0-1.

It was named for Frank Wigglesworth Clarke

Frank Wigglesworth Clarke

Frank Wigglesworth Clarke of Boston, Massachusetts, and Washington, D.C. was an American scientist and chemist. Sometimes known as the "Father of Geochemistry," Clarke is credited with determining the composition of the Earth's crust...

 (1847-1931), American mineral chemist, and former chief chemist of the United States Geological Survey

United States Geological Survey

The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...

.