New Mineral Species for New York State

Five mineral species never before described in New York State
were discovered as a result of recent investigations.

Chevkinite-(Ce)
Monroe, Orange Co.
More on Chevkinite-(Ce)		chevkinite
Ancylite-(Ce)
Manhattan, New York Co.		ancylite
Calcioancylite-(Ce)
Manhattan, New York Co.		calcioancylite
Coffinite on Th-rich Uraninite
Bedford, Westchester Co.		coffinite
Gahnite
Keene, Essex Co.		gahnite

Chevkinite-(Ce)

Chevkinite-(Ce), a Ti and REE silicate with perrierite as its dimorph, has been recently collected in Monroe, Orange Co., New York. The host rock is a pegmatite with acid oligoclase and hornblende. Chevkinite-(Ce) chevkiniteappears as rounded isometric or elongated, dark red-brown patches from 1mm to 1cm in size surrounded by a very thin, white rim mainly composed of cryptocrystalline silica and a mixture of Ti oxide and probably some clay minerals. It occurs as inclusions in oligoclase and hornblende. In some places chevkinite-(Ce) is cut by very narrow veins having the same composition as the surrounding rim. Very rarely, pyrite veinlets cut the host rock and chevkinite-(Ce) patches. Well developed, sometimes pyramidal, double-terminated, reddish-brown, zoned, tetragonal prisms of zircon crystals up to 5 millimeters, accompany it.

Investigation by transmitted light microscopy and X-ray diffraction showed that this chevkinite-(Ce) is completely metamictic and displays a decomposition texture. Electron microprobe analyzes gave the following compositional range:
SiO2 20.34%-25.59%; TiO2 17.66%-18.1 %; Al2O3 3.28%-5%; FeO 4.6%-7.23%;
CaO 3.89%-4.2%; Ce2O3 14.76%-20.63%; La2O3 7.31%-11.07%, Y2O3 0.015%-0.59%,
ThO2 1.96%-2.04%.
The missing percentage appears to be water. The metamictization process could explain the chemical variations and the large amount of water. In order to partially recover the structural pattern, we heated the mineral at 10000C for one hour and a half in a Ni crucible. The d-spacings and intensities, 3.1448 (100), 2.9730 (22), 2.7212 (56), 2.6084 (6), 2.1599 (34), proved the presence of chevkinite-(Ce).

The occurrence of chevkinite-(Ce) at the above mentioned locality may represent a significant fractionated phase in a relatively evolved SiO2-rich magma or in a Ti and REE-saturated residual phase from a low degree melt in a medium-high metamorphic environment. Its crystallization is possible in a magma or residual phase with low Ca and high REE activity where the TiO2 content has not been critically lowered by the earlier precipitation of a Ti mineral.

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