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Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO42. Topaz crystallizes in the orthorhombic system, its crystals are prismatic terminated by pyramidal and other faces, it is one of the hardest occurring minerals and is the hardest of any silicate mineral. This hardness combined with its usual transparency and variety of colors means that it has acquired wide use in jewellery as a cut gemstone as well as for intaglios and other gemstone carvings. Topaz in its natural state is a golden brown to yellow, a characteristic which means it is sometimes confused with the less valuable gemstone citrine. A variety of impurities and treatments may make topaz wine red, pale gray, reddish-orange, pale green, or pink, opaque to translucent/transparent; the pink and red varieties come from chromium replacing aluminium in its crystalline structure. Orange topaz known as precious topaz, is the traditional November birthstone, the symbol of friendship, the state gemstone of the US state of Utah.

Imperial topaz is pink or pink-orange. Brazilian imperial topaz can have a bright yellow to deep golden brown hue, sometimes violet. Many brown or pale topazes are treated to make them bright yellow, pink or violet colored; some imperial topaz stones can fade on exposure to sunlight for an extended period of time. Blue topaz is the state gemstone of the US state of Texas. Occurring blue topaz is quite rare. Colorless, gray or pale yellow and blue material is heat treated and irradiated to produce a more desired darker blue. Mystic topaz is colorless topaz, artificially coated via a vapor deposition process giving it a rainbow effect on its surface. Although hard, topaz must be treated with greater care than some other minerals of similar hardness because of a weakness of atomic bonding of the stone's molecules along one or another axial plane; this gives topaz a tendency to break along such a cleavage plane. Topaz has a low index of refraction for a gemstone, so stones with large facets or tables do not sparkle as as stones cut from minerals with higher refractive indices, though quality colorless topaz sparkles and shows more "life" than cut quartz.

When given a typical "brilliant" cut, topaz may either show a sparkling table facet surrounded by dead-looking crown facets or a ring of sparkling crown facets with a dull well-like table. Topaz is associated with silicic igneous rocks of the granite and rhyolite type, it crystallizes in granitic pegmatites or in vapor cavities in rhyolite lava flows including those at Topaz Mountain in western Utah and Chivinar in South America. It can be found with fluorite and cassiterite in various areas including the Ural and Ilmensky Mountains of Russia, in Afghanistan, Sri Lanka, Czech Republic, Norway, Italy, Japan, Mexico. Brazil is one of the largest producers of topaz, some clear topaz crystals from Brazilian pegmatites can reach boulder size and weigh hundreds of pounds; the Topaz of Aurangzeb, observed by Jean Baptiste Tavernier weighed 157.75 carats. The American Golden Topaz, a more recent gem, weighed a massive 22,892.5 carats. Large, vivid blue topaz specimens from the St. Anns mine in Zimbabwe were found in the late 1980s.

Colorless and light-blue varieties of topaz are found in Precambrian granite in Mason County, Texas within the Llano Uplift. There is no commercial mining of topaz in that area, it is possible to synthesize topaz. However occurring topaz is so abundant that this is not economically viable; the name "topaz" is derived from the Greek Τοπάζιος or Τοπάζιον, from Τοπαζος, the ancient name of St. John's Island in the Red Sea, difficult to find and from which a yellow stone was mined in ancient times. Ancient Sri Lanka exported native oriental topazes to Greece and ancient Egypt, which led to the etymologically related names of the island by Alexander Polyhistor and the early Egyptians – "land of the Topaz". Pliny said that Topazos is a legendary island in the Red Sea and the mineral "topaz" was first mined there. Alternatively, the word topaz may be related to the Sanskrit word तपस् "tapas", meaning "heat" or "fire". Nicols, the author of one of the first systematic treatises on minerals and gemstones, dedicated two chapters to the topic in 1652.

In the Middle Ages, the name topaz was used to refer to any yellow gemstone, but in modern times it denotes only the silicate described above. Many English translations of the Bible, including the King James Version, mention topaz. However, because these translations as topaz all derive from the Septuagint translation topazi, which referred to a yellow stone, not topaz, but chrysolite, topaz is not meant here. An English superstition held that topaz cured lunacy; the ancient Romans believed. During the Middle Ages, it was believed that attaching the topaz to the left arm protected the owner from any curse and warded off the evil eye, it was believed that wearing increased body heat, which would enable people to relieve a cold or fever. In Europe in the Middle Ages, topaz was believed to enhance mental powers. Agate Beryl Opa

Caryocolum spinosum

Mosha River

The Mosha is a river in Plesetsky and Nyandomsky Districts of Arkhangelsk Oblast in Russia. It is a right tributary of the Onega River, it is 131 kilometres long, the area of its basin 8,450 square kilometres. The main tributaries of the Mosha are Iksa River, Lim River, Lepsha River, Lelma River; as a matter of fact, the longest tributary of the Mosha, the Lepsha, is longer than the Mosha itself. The river basin of the Mosha includes all of Nyandomsky District and some areas in Plesetsky, Velsky and Shenkursky Districts. For a river of this length, the watershed area is rather big; the source of the Mosha is Lake Bolshoye Moshenskoye in Nyandomsky District. The Mosha is however only the final part of a longer waterway: Voyezerka River which empties into Lake Bolshoye Moshenskoye has its source in Lake Spasskoye, another major lake in the area, the right tributary of the Voyezerka, Kanaksha River has the length of 98 kilometres. Starting from Lake Bolshoye Moshenskoye, the Mosha flows north-west and soon accepts the Iksa from the left and the Lim from the right.

Downstream, it accepts the Shozhma from the left and the Nimenga from the right. The Mosha crosses the railway line between Konosha and Arkhangelsk at the station of Shalakusha and behind the station accepts the Lepsha from the right, it crosses into Plesetsky District and accepts the Lelma from the left. Close to the mouth, on the right bank of the Mosha there is a big selo of Fedovo; the mouth of the mosha is across the village of Boyarskaya. The upper stretch of the river, close to the Lake Bolshoye Moshenskoye, is populated; the lowest village at this stretch is Malaya Orma. There are no villages between Malaya Orma and Shalakusha, no villages between Shalakusha and Prokhnovo, upstream from Fedovo. There are villages located at some of the tributaries of the Mosha though

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