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The serpentine subgroup (part of the kaolinite-serpentine group) are greenish, brownish, or spotted minerals commonly found in serpentinite rocks. They are used as a source of magnesium and asbestos, and as a decorative stone.〔Serpentine, American Heritage Dictionary〕 The name is thought to come from the greenish color being that of a serpent.〔Serpentine, Encyclopedia Britannica, 1911, s:1911 Encyclopædia Britannica/Serpentine (mineral)〕 The serpentine group describes a group of common rock-forming hydrous magnesium iron phyllosilicate ((, )3) minerals; they may contain minor amounts of other elements including chromium, manganese, cobalt or nickel. In mineralogy and gemology, serpentine may refer to any of 20 varieties belonging to the serpentine group. Owing to admixture, these varieties are not always easy to individualize, and distinctions are not usually made. There are three important mineral polymorphs of serpentine: antigorite, chrysotile and lizardite. The chrysotile group of minerals are polymorphous, meaning that they have the same chemical formulae, but the molecules are arranged into different structures, or crystal lattices.〔Minerals.net, Serpentine, ()〕 Chrysotile with a fiberous habit is one type of asbestos. Other minerals in the chrysotile group may have a platy habit. Many types of serpentine have been used for jewellery and hardstone carving, sometimes under the name ''false jade'' or ''Teton jade''.〔(National Park Service )〕〔Hunter, Sir William Wilson and Burn, Sir Richard, The Imperial Gazeteer of India, Vol. 3, Oxford, England: Clarendon Press, Henry Frowde Publishers (1907), p. 242〕 ==Overview== Their olive green color and smooth or scaly appearance is the basis of the name from the Latin ''serpentinus'', meaning "serpent rock," according to Best (2003). They have their origins in metamorphic alterations of peridotite and pyroxene. Serpentines may also pseudomorphously replace other magnesium silicates. Alterations may be incomplete, causing physical properties of serpentines to vary widely. Where they form a significant part of the land surface, the soil is unusually high in clay. Antigorite is the polymorph of serpentine that most commonly forms during metamorphism of wet ultramafic rocks and is stable at the highest temperatures—to over at depths of or so. In contrast, lizardite and chrysotile typically form near the Earth's surface and break down at relatively low temperatures, probably well below . It has been suggested that chrysotile is never stable relative to either of the other two serpentine polymorphs. Samples of the oceanic crust and uppermost mantle from ocean basins document that ultramafic rocks there commonly contain abundant serpentine. Antigorite contains water in its structure, about 13 percent by weight. Hence, antigorite may play an important role in the transport of water into the earth in subduction zones and in the subsequent release of water to create magmas in island arcs, and some of the water may be carried to yet greater depths. Soils derived from serpentine are toxic to many plants, because of high levels of nickel, chromium, and cobalt; growth of many plants is also inhibited by low levels of potassium and phosphorus and a low ratio of calcium/magnesium. The flora is generally very distinctive, with specialised, slow-growing species. Areas of serpentine-derived soil will show as strips of shrubland and open, scattered small trees (often conifers) within otherwise forested areas; these areas are called serpentine barrens. Most serpentines are opaque to translucent, light (specific gravity between 2.2–2.9), soft (hardness 2.5–4), infusible and susceptible to acids. All are microcrystalline and massive in habit, never being found as single crystals. Luster may be vitreous, greasy or silky. Colours range from white to grey, yellow to green, and brown to black, and are often splotchy or veined. Many are intergrown with other minerals, such as calcite and dolomite. Occurrence is worldwide; New Caledonia, Canada (Quebec), US (northern California, Rhode Island, Connecticut, Massachusetts, Maryland and southern Pennsylvania), Afghanistan, Britain (Cornwall and Ireland), Greece (Thessaly), China, Ural Mountains (Russia), France, Korea, Austria (Styria and Carinthia), India (Assam, and Manipur), Myanmar (Burma), New Zealand, Norway and Italy are notable localities. Serpentines find use in industry for a number of purposes, such as railway ballasts, building materials, and the asbestiform types find use as thermal and electrical insulation (chrysotile asbestos). The asbestos content can be released to the air when serpentine is excavated and if it is used as a road surface, forming a long term health hazard by breathing. Asbestos from serpentine can also appear at low levels in water supplies through normal weathering processes, but there is as yet no identified health hazard associated with use or ingestion. In its natural state, some forms of serpentine react with carbon dioxide and re-release oxygen into the atmosphere. The more attractive and durable varieties (all of antigorite) are termed "noble" or "precious" serpentine and are used extensively as gems and in ornamental carvings. The town of Bhera in the historic Punjab province of the Indian subcontinent was known for centuries for finishing a relatively pure form of green serpentine obtained from quarries in Afghanistan into lapidary work, cups, ornamental sword hilts, and dagger handles.〔 This high-grade serpentine ore was known as ''sang-i-yashm'' or to the English, ''false jade'', and was used for generations by Indian craftsmen for lapidary work.〔〔Watt, Sir George, ''The Commercial Products of India'', London: John Murray Publishers (1908), p. 561〕 It is easily carved, taking a good polish, and is said to have a pleasingly greasy feel.〔''(The Stone Age Jewels: Serpentine )'', retrieved 2 October 2011〕 Less valuable serpentine ores of varying hardness and clarity are also sometimes dyed to imitate jade.〔 Misleading synonyms for this material include "Suzhou jade", "Styrian jade", and "New jade". New Caledonian serpentine is particularly rich in nickel. The Māori of New Zealand once carved beautiful objects from local serpentine, which they called ''tangiwai'', meaning "tears". The ''lapis atracius'' of the Romans, now known as verde antique, or verde antico, is a serpentinite breccia popular as a decorative facing stone. In classical times it was mined at Casambala, Thessaly, Greece. Serpentinite marbles are also widely used: Green ''Connemara marble'' (or ''Irish green marble'') from Connemara, Ireland (and many other sources), and red ''Rosso di Levanto marble'' from Italy. Use is limited to indoor settings as serpentinites do not weather well. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Serpentine subgroup」の詳細全文を読む スポンサード リンク
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