Nelsonite is an igneous rock primarily constituted of ilmenite and apatite, with anatase, chlorite, phosphosiderite, talc and/or wavellite appearing as minor components. Rocks are equigranular with a grain size around 2 – 3 mm.[2] The black ilmenite is slightly magnetic while the whitish apatite is not.[3]
At one time, it was mined for the primary extraction of titanium dioxide. Titanium dioxide from ilmenite is used as a white paint pigments[5] and in the early 1900's as a colorant of artificial teeth.[1][6] The calcium phosphate from apatite is used as agricultural fertilizer.[6] While no active mining of Nelsonite occurs in Virginia, active mining occurs in parts of China for rare-earth elements.[3][6][2]
Anorthosite-related nelsonite occurs mainly as veins and lensoidal intrusions in anorthosite complex or wall rocks.[7] The Fe–Ti–P-rich magma liquids formed immiscible and eutectic mixtures crystallizing around 850-1,000 °C followed by intense fractionation.[8][6]
Disagreement exists on the role liquid immiscibility plays in generating nelsonite and Fe–Ti oxides ore.[7] 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).[7] Nelsonites experience differential weathering. Exposed apatite within the Nelsonite is readily removed through solution by meteoric waters that can result in a cellular or sponge-like ilmenite mass.[1]
Nelsonites are generally associated with anorthosite intrusions and scarce worldwide.
[7] 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.[3]
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.[1]
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.[1]
^ abKolker, Allan (1982). "Mineralogy and Geochemistry of Fe-Ti Oxide and Apatite (Nelsonite) Deposits and Evaluation of the Liquid Immiscibility Hypothesis". Economic Geology. 77 (5): 1146–1158. CiteSeerX10.1.1.918.2121. doi:10.2113/gsecongeo.77.5.1146.
