Garnet details
Natural garnets are divided into the calcium bearing ugrandites, named after the initial letters of the calcium species uvarovite, grossular, and andradite, and the calcium-free pyralspites, named after the members pyrope, almandine, and spessartine. Aluminum, iron, and chromium substitute freely in the ugrandites. Iron, magnesium, and manganese substitute readily for one another in the pyralspites, and all gradations between the pure species are possible.
Much less substitution occurs between the two groups.