Aquamarines are 7.5 to 8 on the Mohs scale. They get their blue color from iron, and the more iron they contain, the higher the color intensity. The stones are of magmatic origin and usually very transparent and pure, i.e. without inclusions or cracks and with an even color distribution. The rare inclusions create a cat's eye or star effect aquamarine. Possible color varieties include pale blue to dark blue and blue-green aquamarines. Intense blue ones are currently the most sought after. Aquamarines are found in pegmatites, especially granites, but also in gneiss and as river sediments. Deposits have been found on all continents except Antarctica, so it is a relatively common variety of beryl. The most important deposits are found in Brazil, especially in the state of Minas Gerais, and in Africa (Mozambique, Nigeria, Kenya). Two of the largest aquamarines ever found come from Brazil: in 1910 a greenish-blue, flawless aquamarine weighing 110.5 kg was found in the Marambaia River, and the largest one found so far comes from the Galilea mine, where it was found in 1992 - it weighed 400 kg. Santa Maria aquamarines, which are named after the mine of the same name and are deep blue in color, are considered to be of particularly high quality. In reference to this, there is also the designation "Santa Maria Africana" for stones from a mine in Mozambique, which strongly resemble the Brazilian ones. Since the intense blue coveted especially for gemstones is rare in naturally occurring stones, stones are improved by firing at temperatures between 400 and 450 degrees Celsius. The fired stones are difficult to distinguish from the unfired ones, but they are sensitive to heat and can lose their color again at about 100 degrees Celsius. Blue topaz, elbaite or zircon might be mistaken for aquamarines, but these three stones have a greater density.