**2.3.4. Fluorbritholite-(Y)**

Britholite-(Y) is very brittle mineral with reddish brown or black color, pale brown streak and resinous luster that crystallizes as hexagonal in the space group P63/M with the unit cell parameters *a* = 9.43 and *c* = 6.81 Å, *a*:*c* = 1:0.722, *V* = 524.45 Å3 and*Z* = 2. Calculated and measured

The mineral fluorbritholite-(Ce) ((Ce,Ca)5(SiO4)3F) [1],[110]) is the fluorine-rich analogue of britholite-(Ce). The structure and known localities of the mineral fluorbritholite-(Ce) are shown in **Fig. 36** and **Fig. 37**, respectively. The mineral has a yellow, reddish-brown color, or

**Fig. 36** The structure (perspective view along the *c*-axis) and the crystal habit of fluorbritholite-(Ce).

**Fig. 37** The localities for the mineral fluorbritholite-(Ce).

densities of the mineral are 4.07 and 4.25 g·cm−3, respectively.

86 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

**2.3.3. Fluorbritholite-(Ce)**

The mineral fluorbritholite-(Y) ((Y,Ca)5(SiO4)3F) [108]) was named as the fluorine-dominant analogue of britholite-(Y), where the Levinson-type suffix modifier, -(Y), indicates the dominance of yttrium among rare-earth elements. It forms irregular grains, hexagonal to tabular crystals and short-prismatic to thick-tabular crystals. The known localities and structures of the mineral fluorbritholite-(Y) are shown in **Fig. 38** and **Fig. 39**, respectively.

**Fig. 38** The structure (perspective view along the *c*-axis) and the crystal habit of fluorbritholite-(Y).

**Fig. 39** The localities for the mineral fluorbritholite-(Y).

The mineral fluorbritholite crystallizes in hexagonal systems of the space group P63/m with the crystallographic parameters of unit cell *a* = 9.444 and *c* = 6.819 Å, *a*:*c* = 1:0.722, *V* = 526.68 Å3 and *Z* = 2. It is a brittle mineral of light-pink or brown color and calculated density of 4.61 g·cm −3. It has a pale brownish or white streak and its hardness on the Mohs scale is 5.
