Emerald is a variety of beryl, a beryllium aluminum cyclosilicate (Be3Al2(SiO3)6) of which the crystal system is hexagonal. They are usually formed in pegmatites, igneous rocks formed during the final stages of a magma's solidification. Varieties of beryl occur in many colors, but emerald always occurs in hues of green, the result of trace amounts of chromium in the composition. When pure and flawless, emerald is the most precious green gemstone known, but they are rarely flawless. Treatments may cover up some flaws, a fact implicating that stones with small flaws are sometimes valued above normal for their authenticity. The emerald crystals are here seen in a quartzite host-rock from pegmatites in the Boyaca region of Colombia. Actual width is 11 mm