Nelsonite is an igneous rock primarily constituted of

ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printi ...

and

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...

, with

anatase Anatase is a metastable mineral form of titanium dioxide (TiO2) with a Tetragonal crystal system, tetragonal crystal structure. Although colorless or white when pure, anatase in nature is usually a black solid due to impurities. Three other Pol ...

chlorite The chlorite ion, or chlorine dioxide anion, is the halite (oxyanion), halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as s ...

, phosphosiderite,

talc Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula . Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant ...

and/or

wavellite Wavellite is an aluminium basic phosphate mineral with formula aluminium, Al3(phosphorus, Poxygen, O4)2(Ohydrogen, H, fluorine, F)3·5water, H2O. Distinct crystals are rare, and it normally occurs as translucent green radial or spherical clusters ...

appearing as minor components. Rocks are equigranular with a grain size around 2 – 3 mm. The black ilmenite is slightly magnetic while the whitish apatite is not.

Name

It was named for

Nelson County, Virginia Nelson County is a county located in the Commonwealth of Virginia, in the United States. As of the 2020 census, the population was 14,775. Its county seat is Lovingston. Nelson County is part of the Charlottesville, VA, Metropolitan Statist ...

, and is also found in that state's Amherst and Roanoke counties. In 2016, the Virginia legislature designated it as the official

State Rock Leaders of states in the U.S. which have significant mineral deposits often create a state mineral, rock, stone or gemstone to promote interest in their natural resources, history, tourism, etc. Not every state has an official state mineral, rock, ...

Virginia Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...

Use

At one time, it was mined for the primary extraction of

titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound derived from titanium with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or Colour Index Internationa ...

. Titanium dioxide from ilmenite is used as a white paint pigments and in the early 1900's as a colorant of artificial teeth. The calcium phosphate from apatite is used as agricultural fertilizer. While no active mining of Nelsonite occurs in Virginia, active mining occurs in parts of China for

rare-earth element The rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), are a set o ...

Formation

Anorthosite-related nelsonite occurs mainly as veins and lensoidal intrusions in anorthosite complex or wall rocks. The Fe–Ti–P-rich magma liquids formed immiscible and eutectic mixtures crystallizing around 850-1,000 °C followed by intense fractionation. Disagreement exists on the role liquid immiscibility plays in generating nelsonite and Fe–Ti oxides ore. It is not common to have such relatively large density differentials of mineral constituents as seen in Nelsonite; ilmenite (4.7–5.2 g/cm³) and apatite (~ 3.5 g/cm³). Nelsonites experience differential weathering. Exposed apatite within the Nelsonite is readily removed through solution by

meteoric water Meteoric water, derived from precipitation such as snow and rain, includes water from lakes, rivers, and ice melts, all of which indirectly originate from precipitation. The journey of meteoric water from the atmosphere to the Earth's surface is a ...

s that can result in a cellular or sponge-like ilmenite mass.

Occurrence

Nelsonites are generally associated with anorthosite intrusions and scarce worldwide. Nelsonite occurs at various localities, not limited to: Nelson, Amherst, & Roanoke Counties, Va.; Carthage & Cheney Pond, N.Y.; Laramie, W.Va.; Washington State; Quebec, Canada; and China.

Roseland-Piney River district, Virginia

The nelsonite occurs in alkalic Roseland anorthosite, and in gneiss, granulite, and charnockitic rocks surrounding the anorthosite. Multiple varieties of equigranular nelsonite are present in the Roseland-Piney River district. * Ilmenite nelsonite: the most abundant variety, commonly occurs in marginal parts of the anorthosite and in surrounding rocks near the anorthosite contact. * rutile nelsonite: occurs only within the anorthosite. * magnetite and biotite nelsonite: limited to the rocks surrounding the Roseland anorthosite. * hornblende nelsonite * gabbro-nelsonite: a rock intermediate in composition between gabbro and nelsonite The prefixes ilmenite, rutile, magnetite, biotite, and hornblende denote special richness of the rocks in these minerals.

References

{{reflist Igneous rocks Symbols of Virginia Nelson County, Virginia