Trachyte (from the Greek. Τραχύς - rough, uneven) is an igneous volcanic rock of medium composition , a moderately alkaline alkalinity series from the trachyte family. It is an effusive analogue of syenite . Unchanged (kainotype) breed. The main component is potassium feldspar , prevailing over acidic plagioclase ; of the dark-colored minerals present in a small amount of biotite , as well as amphibole and pyroxene . The phenocrysts are represented by the glassy sanidine , the less acidic plagioclase, and from the dark-colored ones, by biotite and amphibole .
Color - grayish white, gray, pinkish, yellowish or brownish. Structure - porphyritic , cryptocrystalline. The texture is banded, porous, fluid. Specific weight - 2.5 g / cm ³.
The occurrence forms are streams , domes, thyroid volcanoes , small hypabyssal intrusions and dikes . Separately columnar.
The average chemical composition . SiO 2 58-64%, TіO 2 0.5-1%, Al 2 O 3 15-20%, Fe 2 O 3 2-3%, FeO 2-3%, MgO 1-2%, CaO 2-4%, Na 2 O 3-6%; K 2 O 4-6%. [one]
Among the trachyte rocks with a high silica content, quartz trachytes are distinguished with an SiO 2 content of 62-67%, as well as rocks transitional between trachytes and rhyolites — trachyryolites , dacites — trachydocytes , and rhyodacites — trachiriodocytes .
Content
Diagnostics
They are macroscopically very similar to rhyolites , but differ from them in the absence of porphyritic silica . They have a rough break .
Deposits
Belarus , Czech Republic , France , Northern Italy , Azerbaijan, Armenia , the Northern Caucasus, etc.
Practical value
Beautifully colored trachyte is an ornamental and ornamental stone.
Notes
- ↑ Petrographic Code of Russia. - SPb .: VSEGEI, 2008. - p. 134. - 200 p. - 1 500 copies - ISBN 978-5-93761-106-2
Links
- Trachit // Great Soviet Encyclopedia : [in 30 t.] / Ch. ed. A. M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.