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.
Both the variance and the standard deviation meet these three criteria for normally-distributed (symmetric, bell-curve) data sets. The variance (Ï2) is a measure of how far each value in the data set is from the mean. Here is how it is defined: 1  Subtract the mean from each value in the data. 2  This gives you a measure of the distance of each value from the mean.