Guide to Mineral Sizes
MM - Micromineral - a small (typically less than 1") piece of matrix with micro xtls. Unmounted. Strictly speaking, the term "micromineral" depends more on the size of the crystals (or other point of interest) than it does on the size of the matrix.
MT - Micromount - a mounted micro specimen, usually in a standard "micromount" size box. The matrix, where present, is typically 3/8 inch or less in max. dimension. Some micromounts may consist of a single crystal mounted with no matrix.
TN - Thumbnail - fits in a 1.25" x 1.25" x 1.25" box (a standard "Perky" box).
MIN - Miniature - size ranging from about 1.5 inches to about 2.5 inches across max. dimension.
SMC - Small cabinet - 2.5 to 4 inches across max. dimensions.
LGC - Max. dimension of 4" to 6".
MUS - Max. dimension of 6" or greater.
These size classifications are not absolute; different dealers may have slightly different cutoff points for what they consider to be "miniature", "small cabinet", and so on. The definitions for TN and MT sized minerals are fairly standard, however, because the box size constrains them.
Most of the MM and MT size minerals are on their own page.
See below for more categories.
Minerals, Various, A thru L
Minerals, Various, M thru Z