SiO 2. One of the most common minerals in the world, quartz can be found in sedimentary, metamorphic, and igneous rocks throughout Virginia. Quartz typically appears as clear or whitish crystals within a rock such as granite.Amethyst, agate, chalcedony, chert (flint), and opal are all varieties of quartz.iO 2. One of the most common minerals in the world, quartz can be found in sedimentary, metamorphic, and igneous rocks throughout Virginia. Quartz typically appears as clear or whitish crystals within a rock such as granite.
In statistics, the standard deviation is a very common measure of dispersion. Standard deviation measures how spread out the values in a data set are around the mean. More precisely, it is a measure of the average distance between the values of the data in the set and the mean.
1 Remember, variance is how spread out your data is from the mean or mathematical average. 2  Standard deviation is a similar figure, which represents how spread out your data is in your sample.  In our example sample of test scores, the variance was 4.8.