BERYL (EMERALD, MARYN, HELIODOR, MORGANIT, GOSZENIT).
Transparent varieties of beryl, thanks to their beautiful colors and high hardness, are highly valued as precious stones. The most important noble varieties of beryl are: green emerald, cyan - aquamarine, yellow - heliodor (golden beryl), pink - morganite (worobiewit) and colorless goshenite.
Chemical properties. Beryl is a silicate of the elements beryllium and aluminum with the formula Al2Be3 [And6O18]. Sometimes alkaline elements are present in the form of admixtures: sodium, potassium, lit, rubid i cez. These elements come in colorless and pink varieties. The green color of the emerald is caused by the admixture of chromium. Beryllium does not melt in the flame of the blower, only the edges of its crumbs are rounded. Transparent varieties become cloudy at high temperatures. Beryllium does not dissolve in acids.
Character. Beryllium crystals belong to the hexagonal system. They are often well educated and sometimes of considerable size. The most common forms are hexagonal poles and base double-walled poles; double pyramids are less common. Beryllium usually comes in the form of single crystals, only occasionally it forms stamen clusters.
The structure of beryllium is very characteristic. Tetrahedra [SiO4] form hexagonal rings [And6O18]12– stacked on top of each other in the direction of the major axis. Aluminum cations Al3+ and beryllium Be2+ are arranged between the rings in this way, that Al3+ is surrounded by six, a Be2+ four oxygen atoms. There are hollow channels inside the hexagonal rings, which may contain the atoms of the elements additionally included in beryllium: litu Li, cesium Cs, sodu Na, potassium K and fluorine F and hydroxyl groups OH.
Beryllium crystals are sometimes very large. Real giants were found in the US in the states of Maine, New Hampshire i Massachusetts. Biggest, about the length 6 m and width 1 m, come from Albany, Maine; one of them weighed 19 t. Similarly, giant beryllium crystals have also been found in southwestern Africa (Namakwaland). These giant beryllium crystals are not transparent and are not used for ornamental purposes. There are also very large crystals among the transparent varieties. W 1910 r. perfectly clear aquamarine with a beautiful blue color has been found in southern Brazil, half a meter long and weighing more than 100 kg. Cut into small pieces, it served the needs of the global jewelery market for three years.
Beryllium crystal lattice: a - vertical projection, b - projections on the ground plane - perpendicular to the 6-fold axis.
Physical properties. Beryl has not very pronounced cleavage parallel to the base wall and to the walls of the column. Break uneven, often seashell. Hardness 7.5-8. Density 2.6-2.8 g / cm³. Regular beryllium is most often pale green in color, yellowish or grayish white. Transparent varieties are green, blue, yellow, pink or colorless. The gloss is glassy.
Beryl is optically uniaxial. The refractive indices have clearly variable values: nω = 1,568 – 1,598, nε = 1,564 – 1,590. Double light refraction is low (0,004 – 0,008), optical nature negative. Dispersion is weak (0,014). The degree of dichroism depends on the color; it is especially strong in the emerald. Dychroism, apparently in directions perpendicular to the main axis of the crystals, depends on the color of the stone.
Low refractive indexes and low dispersion of beryllium contribute to its relatively low gloss and no fire. Transparent varieties are valued mainly for their beautiful color.
Occurrence. Beryllium is the most common mineral containing the beryllium element. After the war, interest in this mineral grew due to the use of beryllium as an admixture in various alloys and the use of atomic energy. This resulted in a significant increase in the extraction of beryllium and the discovery of new deposits. The largest deposits of beryllium are in North America (United States and Canada) and South (Colombia, Brazil, Argentina) and in various parts of Africa (Zaire, Egypt, Uganda, South Africa, Namibia, Madagascar) and in the Soviet Union, Indian, southern Australia. Beryllium is also found in small amounts in Europe: in Portugal, Spain, Czechoslovakia, RFN, Romania, Norway and Italy.
Beryllium is most often found in granite pegmatite veins, on the walls of the vacuum in granites, in rocks transformed pneumatolytically (grejzen), and also as a component of some metamorphic rocks (mica shales, transformed limestones), and in secondary deposits in sand and gravel.
Beryls can also be found in the granite massifs of Lower Silesia. However, they are usually opaque beryllium. They occur mainly in granite pegmatites, e.g.. in the vicinity of Strzegom. Yellowish or blue-green crystals can be found near Ząbkowice Śląskie, up to several centimeters in length.