**1.6.7. Mimetite and clinomimetite**

Mimetite (arsenopyromorphite, lead chloroarsenate, mimetite-H, Pb5(AsO4)3Cl ) [45],[55], [181],[182]), is the end memberin the ternary system pyromorphite–vanadinite–mimetite. This is also the reason why the name of mineral is derived from Greek word "*mimethes*," i.e. the imitator. Mimetite is also Pb5 analogue of hedyphane (**Section 2.1**). Mimetite (**Fig. 33**) is an arsenate mineral; it usually forms as a secondary mineral in lead deposits through the oxidation of galena (PbS [183], Gn50) and arsenates [184].

**Fig. 33.** Mimetite (Příbram, Czech Republic).

Mimetite usually crystallizes in oxidized zones of lead deposits as small hexagonal prism with colors ranging from pale to bright yellow, orange, yellowish-brown, white, translucent, to opaque [184]. In accordance with other hexagonal apatite-group minerals, it crystallizes in the space group P63/M. The unit cell parameters are *a* = 10.46, *c* = 7.44 Å, *a*:*c* = 1:0.71 *Z* = 2 and *V* = 704.96 Å3 . The calculated density is 7.10 g·cm−3. The hardness of the mineral on the Mohs scale is in the range from 3½ to 4. The structure and the shape of mimetite crystal is shown in **Fig. 34**.

**Fig. 34.** The structure (perspective view along the *c*-axis) and the shape of mimetite crystal of hexagonal (a) and mono‐ clinic polymorph (b).

<sup>50</sup> Symbol of mineral for rock- and ore-forming minerals.

The polymorphs of mimetite51 are the monoclinic mimetite–M formerly known as clinomime‐ tite mineral [185],[186] and mimetite-*2M*[182]. Monoclinic mimetite–Mcrystallizes in the space group P21/B with the crystallographic parameters *a* = 10.189, *b* = 20.371 and *c* = 7.46 Å; angles *α* = *β* = 90° and *γ* = 119.88°; *V* = 1342.57 Å3 ; and *Z* = 4. It is brittle mineral with the hardness of 4 (Mohs scale). The color of mimetite–M is pale greenish, yellow or white, and the mineral has white streak. Measured and calculated densities of the mineral are 7.36 and 7.37 g·cm−3, respectively. Monoclinic polymorphs of mimetite-2M crystallize in the space group of P21 with the crystallographic parameters *a* = 20.422, *b* = 7.438 and *c* = 20.435 Å; ratio *a*:*b*:*c* = 2.746:1:2.747; angles *α* = *β* = 90° and *γ* = 119.95°; *V* = 2689.5 Å3 ; and *Z* = 8.
