Snow quartz correctly known as milk or milky quartz is one of the most common varieties of the mineral quartz. It can be found in almost every rock type and its chemical composition is no different to other varieties of quartz. Its greyish white colour and/or cloudy appearance is caused by microscopic impurities of fluids that became embedded within the crystal during the early stages of its formation.
In its purest form quartz is colourless and transparent but various impurities cause crystals to change colour. An example is amethyst whose purple colour is caused primarily by iron although heat usually in the form of radiation is also required for the transformation to take place. Were it not for the impurities, snow quartz would actually be clear colourless quartz.
Milky quartz can often be found as phantoms within other quartz minerals particularly colourless and translucent varieties. Some would describe it as being an imperfect stone because its cloudy appearance spoils what could otherwise be an almost perfect crystal.
Snow quartz is a trade name mostly used for material that's cut and polished for decorative purposes. Occasionally cut into gemstones, it can be translucent to opaque and is sometimes mistaken for white moonstone. Although the colour can be similar it does not exhibit iridescence. Snow quartz is widely used for tumbled stones and ornamental carvings.