Transparency measures the degree of light that passes through a gemstone. Transparency of a mineral is closely related to factors such as amount of impurities, inclusions or cleavages. For example, in a 1 cm thick gemstone slice, if light can easily pass through it, then it can be said that the gemstone is transparent; examples of transparent gemstones are diamonds, corundum and quartz crystals; if only a little light passes through, then it is said to be translucent; garnet, tourmaline, jadeite and nephrite are some of the translucent minerals. If the light cannot pass through at all, then it is said to be opaque; turquoise, lapis lazuli and most of the organic gemstones opaque minerals. Gemstone minerals usually have weaker light absorption and reflectance, so they appear mostly transparent or translucent. The degree of transparency in a same type of gemstone may also differ by geographic regions or mining deposits. The degree of transparency and internal imperfections are important factors that determine the quality of a gemstone.