Original paper

Calcio-ancylite-(Ce) from syenite pegmatite at Tvedalen, Oslo Region, Norway

Larsen, A.O.; Gault, R.A.


The relatively rare mineral calcio-ancylite-(Ce) has been found in abundance in a syenite pegmatite at Tuften larvikite quarry at Tvedalen, Oslo Region, Norway. The mineral formed as a result of hydrothermal alteration of fluorapatite, and occurs as crystal aggregates in hollow, tubular casts after apatite crystals. The mode of occurrence and paragenesis are described. Prismatic calcio-ancylite-(Ce) crystals may attain 1mm in length, dominated by a prism {120} and terminated by a dipyramid assigned as {477} or {122}, sometimes modified by a small rhombic prism {101}. The mineral is white through pale yellowish brown to pale pink. The unit cell dimensions are a = 7.2790(9), b = 8.5471(9), c = 5.0238(8)Å and V = 312.55(5)Å3. Electron microprobe analyses show that the mineral is chemically inhomogeneous, with Ca/Sr ratios ranging from 1.01 to 5.12. Ce is the dominating rare earth element. A general chemical formula for all ancylite group minerals is proposed: (M2+)1+x(REE)3-x(CO3)4(OH)3-x·(1+x)H2O, where x may vary between -1 and +1. This formula also includes kozoite-(Nd), where x = -1.


calcio-ancylite-cefluorapatite precursorchemical compositionsyenite pegmatitetvedalenoslo regionnorway