Gananite
Gananite (simplified Chinese:赣南矿; traditional Chinese:贛南礦; pinyin:gàn nán kuàng) is a rare bismuth fluoride mineral with a general formula of BiF3. Gananite is an isotropic mineral, it belongs to the space group P43m. This means that Gananite does not show any colors in cross polarized light, because when polarized light passes through it, it does not split into two perpendicular rays. In other words, because Gananite is an isometric mineral, it does not exhibit double refraction. Moreover, this tells us that this mineral is not birefringent. Its color in Plane polarized light is blackish-brown, and it does not show pleochroism.