This is usually referred to as included crystal, but listed on GIA reports as crystal. A crystal is a very common type of inclusion and as its name implies, it is a separate mineral body existing inside of a diamond. More than two dozen types of crystal inclusions have been identified, but by far the most common is diamond itself. Occasionally peridot and garnet occur, but for the most part, you will see small individual diamond crystals that are sometimes small enough to appear as bubbles. Gas bubbles do not occur in diamonds as they do in some natural and synthetic gemstones. When these mistaken bubbles are magnified at higher power, their crystalline geometric shapes become apparent. Carbon spots do occur occasionally in diamond, but again these are often mistaken for dark included crystals. Crystals generally are white to dark brown or gray in color.