Obsidian
General
CategoryVolcanic glass
Identification
Colorusually black; sometimes green or brown; rarely yellow, orange, red or blue[1]
FractureConchoidal
Mohs scale hardness5–6[2]
LusterVitreous
Specific gravityc. 2.4[3]
Optical propertiesTranslucent
Other characteristicsTexture: Smooth; glassy
References[4]

Obsidian (/əbˈsɪdi.ən, ɒb-/)[5] is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock.[6]

Obsidian is produced from felsic lava, rich in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows. These flows have a high content of silica, granting them a high viscosity. The high viscosity inhibits diffusion of atoms through the lava, which inhibits the first step (nucleation) in the formation of mineral crystals. Together with rapid cooling, this results in a natural glass forming from the lava.[7]

Obsidian is hard, brittle, and amorphous; it therefore fractures with sharp edges. In the past, it was used to manufacture cutting and piercing tools, and it has been used experimentally as surgical scalpel blades.[8]

Origin and properties

Obsidian talus at Obsidian Dome, California
Polished snowflake obsidian, formed through the inclusion of cristobalite crystals

The Natural History by the Roman writer Pliny the Elder includes a few sentences about a volcanic glass called obsidian (lapis obsidianus), discovered in Ethiopia by Obsidius, a Roman explorer.[9][10][11][12]

Obsidian is formed from quickly cooled lava, which is the parent material.[13][14][15] Extrusive formation of obsidian may occur when felsic lava cools rapidly at the edges of a felsic lava flow or volcanic dome, or when lava cools during sudden contact with water or air. Intrusive formation of obsidian may occur when felsic lava cools along the edges of a dike.[16][17]

Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions,[18] though few scientists now adhere to this hypothesis.[19]

Obsidian is mineral-like, but not a true mineral because, as a glass, it is not crystalline; in addition, its composition is too variable to be classified as a mineral. It is sometimes classified as a mineraloid.[20] Though obsidian is usually dark in color, similar to mafic rocks such as basalt, the composition of obsidian is extremely felsic. Obsidian consists mainly of SiO2 (silicon dioxide), usually 70% by weight or more. Crystalline rocks with a similar composition include granite and rhyolite. Because obsidian is metastable at the Earth's surface (over time the glass devitrifies, becoming fine-grained mineral crystals), obsidian older than Miocene in age is rare. Exceptionally old obsidians include a Cretaceous welded tuff and a partially devitrified Ordovician perlite.[21] This transformation of obsidian is accelerated by the presence of water. Although newly formed obsidian has a low water content, typically less than 1% water by weight,[22] it becomes progressively hydrated when exposed to groundwater, forming perlite.

Pure obsidian is usually dark in appearance, though the color varies depending on the impurities present. Iron and other transition elements may give the obsidian a dark brown to black color. Most black obsidians contain nanoinclusions of magnetite, an iron oxide.[23] Very few samples of obsidian are nearly colorless. In some stones, the inclusion of small, white, radially clustered crystals (spherulites) of the mineral cristobalite in the black glass produce a blotchy or snowflake pattern (snowflake obsidian). Obsidian may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being cooled. These bubbles can produce interesting effects such as a golden sheen (sheen obsidian). An iridescent, rainbow-like sheen (fire obsidian) is caused by inclusions of magnetite nanoparticles creating thin-film interference.[24] Colorful, striped obsidian (rainbow obsidian) from Mexico contains oriented nanorods of hedenbergite, which cause the rainbow striping effects by thin-film interference.[23]

Occurrence

Glass Mountain, a large obsidian flow at Medicine Lake Volcano in California

Obsidian is found near volcanoes in locations which have undergone rhyolitic eruptions. It can be found in Argentina, Armenia, Azerbaijan, Australia,[25] Canada, Chile, Georgia, Ecuador, El Salvador, Greece, Guatemala, Hungary, Iceland, Indonesia, Italy, Japan, Kenya, Mexico, New Zealand, Papua New Guinea, Peru, Russia, Scotland, the Canary Islands, Turkey and the United States. Obsidian flows which may be hiked on are found within the calderas of Newberry Volcano and Medicine Lake Volcano in the Cascade Range of western North America, and at Inyo Craters east of the Sierra Nevada in California. Yellowstone National Park has a mountainside containing obsidian located between Mammoth Hot Springs and the Norris Geyser Basin, and deposits can be found in many other western U.S. states including Arizona, Colorado, New Mexico, Texas, Utah, and Washington,[26] Oregon[27] and Idaho.

There are only four major deposit areas in the central Mediterranean: Lipari, Pantelleria, Palmarola and Monte Arci (Sardinia).[28]

Ancient sources in the Aegean were Milos and Gyali.[29]

Acıgöl town and the Göllü Dağ volcano were the most important sources in central Anatolia, one of the more important source areas in the prehistoric Near East.[30][31][32]

Prehistoric and historical use

Obsidian arrowhead

The first known archaeological evidence of usage was in Kariandusi (Kenya) and other sites of the Acheulian age (beginning 1.5 million years BP) dated 700,000 BC, although only very few objects have been found at these sites relative to the Neolithic.[33][34][35][36][37] Manufacture of obsidian bladelets at Lipari had reached a high level of sophistication by the late Neolithic, and was traded as far as Sicily, the southern Po river valley, and Croatia.[38] Obsidian bladelets were used in ritual circumcisions and cutting of umbilical cords of newborns.[39] Anatolian sources of obsidian are known to have been the material used in the Levant and modern-day Iraqi Kurdistan from a time beginning sometime about 12,500 BC.[40] Obsidian artifacts are common at Tell Brak, one of the earliest Mesopotamian urban centers, dating to the late fifth millennium BC.[41] Obsidian was valued in Stone Age cultures because, like flint, it could be fractured to produce sharp blades or arrowheads in a process called knapping. Like all glass and some other naturally occurring rocks, obsidian breaks with a characteristic conchoidal fracture. It was also polished to create early mirrors. Modern archaeologists have developed a relative dating system, obsidian hydration dating, to calculate the age of obsidian artifacts.

Europe

Obsidian artifacts first appeared in the European continent in Central Europe in the Middle Paleolithic and had become common by the Upper Paleolithic, although there are exceptions to this. Obsidian played an important role in the transmission of Neolithic knowledge and experiences. The material was mainly used for production of chipped tools which were very sharp due to its nature. Artifacts made of obsidian can be found in many Neolithic cultures across Europe. The source of obsidian for cultures inhabiting the territory of and around Greece was the island of Milos; the Starčevo–Körös–Criș culture obtained obsidian from sources in Hungary and Slovakia, while the Cardium-Impresso cultural complex acquired obsidian from the island outcrops of the central Mediterranean. Through trade, these artifacts ended up in lands thousands of kilometers away from the original source; this indicates that they were a highly valued commodity.[42] John Dee had a mirror, made of obsidian, which was brought from Mexico to Europe between 1527 and 1530 after Hernando Cortés's conquest of the region.[43]

Middle East and Asia

Obsidian tools from Tilkitepe, Turkey, 5th millennium BC. Museum of Anatolian Civilizations

In the Ubaid in the 5th millennium BC, blades were manufactured from obsidian extracted from outcrops located in modern-day Turkey.[44] Ancient Egyptians used obsidian imported from the eastern Mediterranean and southern Red Sea regions. In the eastern Mediterranean area the material was used to make tools, mirrors and decorative objects.[45]

The use of obsidian tools was present in Japan near areas of volcanic activity.[46][47] Obsidian was mined during the Jōmon period.

Obsidian has also been found in Gilat, a site in the western Negev in Israel. Eight obsidian artifacts dating to the Chalcolithic Age found at this site were traced to obsidian sources in Anatolia. Neutron activation analysis (NAA) on the obsidian found at this site helped to reveal trade routes and exchange networks previously unknown.[48]

Americas

Obsidian worked into plates and other wares by Victor Lopez Pelcastre of Nopalillo, Epazoyucan, Hidalgo. On display at the Museo de Arte Popular, Mexico City.

Lithic analysis helps to understand pre-Hispanic groups in Mesoamerica. A careful analysis of obsidian in a culture or place can be of considerable use to reconstruct commerce, production, and distribution, and thereby understand economic, social and political aspects of a civilization. This is the case in Yaxchilán, a Maya city where even warfare implications have been studied linked with obsidian use and its debris.[49] Another example is the archeological recovery at coastal Chumash sites in California, indicating considerable trade with the distant site of Casa Diablo, California in the Sierra Nevada Mountains.[50]

Raw obsidian and obsidian blades from the Mayan site of Takalik Abaj

Pre-Columbian Mesoamericans' use of obsidian was extensive and sophisticated; including carved and worked obsidian for tools and decorative objects. Mesoamericans also made a type of sword with obsidian blades mounted in a wooden body. Called a macuahuitl, the weapon could inflict terrible injuries, combining the sharp cutting edge of an obsidian blade with the ragged cut of a serrated weapon. The polearm version of this weapon was called tepoztopilli.

Obsidian mirrors were used by some Aztec priests to conjure visions and make prophecies. They were connected with Tezcatlipoca, god of obsidian and sorcery, whose name can be translated from the Nahuatl language as 'Smoking Mirror'.[43]

Obsidian imported from Milos, found in Minoan Crete

Indigenous people traded obsidian throughout the Americas. Each volcano and in some cases each volcanic eruption produces a distinguishable type of obsidian allowing archaeologists to use methods such as non-destructive energy dispersive X-ray fluorescence to select minor element compositions from both the artifact and geological sample to trace the origins of a particular artifact.[51] Similar tracing techniques have also allowed obsidian in Greece to be identified as coming from Milos, Nisyros or Gyali, islands in the Aegean Sea. Obsidian cores and blades were traded great distances inland from the coast.[52]

In Chile obsidian tools from Chaitén Volcano have been found as far away as in Chan-Chan 400 km (250 mi) north of the volcano, and also in sites 400 km south of it.[53][54]

Oceania

The Lapita culture, active across a large area of the Pacific Ocean around 1000 BC, made widespread use of obsidian tools and engaged in long distance obsidian trading. The complexity of the production technique for these tools, and the care taken in their storage, may indicate that beyond their practical use they were associated with prestige or high status.[55]

Obsidian was also used on Rapa Nui (Easter Island) for edged tools such as Mataia and the pupils of the eyes of their Moai (statues), which were encircled by rings of bird bone.[56] Obsidian was used to inscribe the Rongorongo glyphs.

Current use

Obsidian can be used to make extremely sharp knives, and obsidian blades are a type of glass knife made using naturally occurring obsidian instead of manufactured glass. Obsidian is used by some surgeons for scalpel blades, although this is not approved by the US Food and Drug Administration (FDA) for use on humans.[57] Well-crafted obsidian blades, like any glass knife, can have a cutting edge many times sharper than high-quality steel surgical scalpels: the cutting edge of the blade is only about three nanometers thick.[58] All metal knives have a jagged, irregular blade when viewed under a strong enough microscope; however, obsidian blades are still smooth, even when examined under an electron microscope.[59] One study found that obsidian incisions produced fewer inflammatory cells and less granulation tissue in a group of rats after seven days but the differences disappeared after twenty-one days.[60] Don Crabtree has produced surgical obsidian blades and written articles on the subject.[58] Obsidian scalpels may be purchased for surgical use on research animals.[61]

The major disadvantage of obsidian blades is their brittleness compared to those made of metal,[62] thus limiting the surgical applications for obsidian blades to a variety of specialized uses where this is not a concern.[58]

Pig carved in snowflake obsidian, 10 centimeters (4 in) long. The markings are spherulites.

Obsidian is also used for ornamental purposes and as a gemstone.[63] It presents a different appearance depending on how it is cut: in one direction it is jet black, while in another it is glistening gray. "Apache tears" are small rounded obsidian nuggets often embedded within a grayish-white perlite matrix.

Plinths for audio turntables have been made of obsidian since the 1970s, such as the grayish-black SH-10B3 plinth by Technics.

See also

References

  1. ↑ King, Hobart M. "Obsidian". Geology.com. Retrieved 3 February 2023.
  2. ↑ Peter Roger Stuart Moorey (1999). Ancient Mesopotamian Materials and Industries: the archaeological evidence. Eisenbrauns. pp. 108–. ISBN 978-1-57506-042-2.
  3. ↑ Ericson, J.E.; Makishima, A.; Mackenzie, J.D.; Berger, R. (January 1975). "Chemical and physical properties of obsidian: a naturally occurring [sic] glass". Journal of Non-Crystalline Solids. 17 (1): 129–142. Bibcode:1975JNCS...17..129E. doi:10.1016/0022-3093(75)90120-9.
  4. ↑ Obsidian, Mindat.org
  5. ↑ "obsidian". Dictionary.com Unabridged (Online). n.d.
  6. ↑ Rafferty, John P. (2012). Rocks (1st ed.). New York, NY: Britannica Educational Pub. in association with Rosen Educational Services. p. 97. ISBN 9781615304929.
  7. ↑ Raymond, Loren A. (1995). Petrology : the study of igneous, sedimentary, metamorphic rocks. Dubuque, IA: Wm. C. Brown. p. 27. ISBN 0697001903.
  8. ↑ Brian Cotterell; Johan Kamminga (1992). Mechanics of pre-industrial technology: an introduction to the mechanics of ancient and traditional material culture. Cambridge University Press. pp. 127–. ISBN 978-0-521-42871-2. Retrieved 9 September 2011.
  9. ↑ Dictionary of Greek and Roman Biography and Mythology, vol. III, p. 2 ("Obsidius").
  10. ↑ obsidian. The Concise Oxford Dictionary of English Etymology. Oxford University Press (1996). Retrieved 2011-11-20.
  11. ↑ D Harper. obsidian. Etymology online. 2012-06-17
  12. ↑ M H Manser. The Facts On File Dictionary of Allusions. Infobase Publishing, 2008, ISBN 0816071055.
  13. ↑ M E Malainey. A Consumer's Guide to Archaeological Science: Analytical Techniques, Springer, 2010 ISBN 1441957030
  14. ↑ P L Barnes-Svarney; T E Svarney (2004). The Handy Geology Answer Book. Visible Ink Press. p. 123. ISBN 978-1578591565.
  15. ↑ M Martini; M Milazzo; M Piacentini; Società Italiana di Fisica (2004). Physics Methods in Archaeometry. Vol. 154. IOS Press. ISBN 978-1586034245.
  16. ↑ Putnam, William C. (1938). "The Mono Craters, California". Geographical Review. 28 (1): 68–82. doi:10.2307/210567. JSTOR 210567. S2CID 163772761.
  17. ↑ Binder, Didier; Gratuze, Bernard; Mouralis, Damase; Balkan-Atlı, Nur (1 December 2011). "New investigations of the Göllüdağ obsidian lava flows system: a multi-disciplinary approach". Journal of Archaeological Science. 38 (12): 3174–3184. doi:10.1016/j.jas.2011.05.014.
  18. ↑ O'Keefe, John A. (1978). "The Tektite Problem". Scientific American. Munn & Company. 239 (2): 116–127. Bibcode:1978SciAm.239b.116O. doi:10.1038/scientificamerican0878-116. JSTOR 24960359.
  19. ↑ Sevigny, Melissa L. (2016). Under desert skies : how Tucson mapped the way to the Moon and planets. Tucson: Sentinel Peak. p. 93. ISBN 9781941451045.
  20. ↑ Pan Ming Huang; Yuncong Li; Malcolm E. Sumner, eds. (2012). Handbook of Soil Sciences: Properties and Processes (Second ed.). Boca Raton: CRC Press. pp. 20–24. ISBN 978-1-4398-0306-6.
  21. ↑ Marshall, Royal R. (1 October 1961). "Devitrification of Natural Glass". GSA Bulletin. 72 (10): 1493–1520. Bibcode:1961GSAB...72.1493M. doi:10.1130/0016-7606(1961)72[1493:DONG]2.0.CO;2.
  22. ↑ "Perlite – Mineral Deposit Profiles". B.C. Geological Survey. Archived from the original on 2008-05-09. Retrieved 2007-11-20.
  23. 1 2 Ma, Chi; Rossman, George (2013). "Nanomineralogy of Gemstones: From Genesis to Discovery" (PDF). Mineralogical Magazine. 77 (5): 1661. doi:10.1180/minmag.2013.077.5.13. hdl:10174/9676. Retrieved May 1, 2019.
  24. ↑ Nadin, E. (2007). "The secret lives of minerals" (PDF). Engineering & Science (1): 10–20.
  25. ↑ Bonetti, R.; Di Cesare, P.; Guglielmetti, A.; Malerba, F.; Migliorini, E.; Oddone, M.; Bird, J. R.; Torrence, R.; Bultitude, R. J. (25 November 1998). "Fission track dating of obsidian source samples from the Willaumez Peninsula, Papua New Guinea and eastern Australia" (PDF). Records of the Australian Museum. 50 (3): 277–84. doi:10.3853/j.0067-1975.50.1998.1286.
  26. ↑ Washington Obsidian Source Map Archived 2015-08-21 at the Wayback Machine. Obsidianlab.com. Retrieved on 2011-11-20.
  27. ↑ Oregon Obsidian Sources. Sourcecatalog.com (2011-11-15). Retrieved on 2011-11-20.
  28. ↑ Iain Morley and Colin Renfrew. The Archaeology of Measurement: Comprehending Heaven, Earth and Time in Ancient Societies, Cambridge University Press, 2010 ISBN 0521119901.
  29. ↑ E Blake; A B Knapp (2005). The Archaeology Of Mediterranean Prehistory. John Wiley & Sons. ISBN 978-0631232681.
  30. ↑ Prince Mikasa no Miya Takahito. Essays on Anatolian Archaeology, Otto Harrassowitz Verlag, 1993 ISBN 3447033959.
  31. ↑ L Romano. 6 ICAANE, Otto Harrassowitz Verlag, 2010 Volume 3 of Proceedings of the 6th International Congress of the Archaeology of the Ancient Near East: 5–10 May 2009 ISBN 3447062177.
  32. ↑ P R S Moorey. Ancient Mesopotamian Materials and Industries: The Archaeological Evidence Eisenbrauns, 1999 ISBN 1575060426.
  33. ↑ Bunny, Sarah (18 April 1985). "Ancient trade routes for obsidian". New Scientist.
  34. ↑ Schmandt-Besserat, D. (1979). Early technologies. Vol. 3. Malibu, Ca.: Undena Publications. ISBN 0890030316.
  35. ↑ Merrick, H.V.; Brown, F.H.; Nash, W.P. (1994). Society, Culture, and Technology in Africa Import. Vol. 11. Univ Museum Pubns. ISBN 1931707057.
  36. ↑ J. D. Fage. The Cambridge history of Africa: From c. 1600 to c. 1790, Part 1050, Cambridge University Press, 1979 ISBN 0521215927
  37. ↑ National Museum of Kenya. Kariandusi Archived 2007-10-24 at the Wayback Machine. Retrieved 2012-06-30
  38. ↑ Martinelli, Maria Clara; Tykot, Robert H.; Vianello, Andrea (20 April 2019). "Lipari (Aeolian islands) obsidian in the late Neolithic. Artifacts, supply, and function". Open Archaeology. 5 (1): 46–64. doi:10.1515/opar-2019-0005. S2CID 150094926.
  39. ↑ Brown, Keri A.; Tykot, Robert H. (August 2018). "Obsidian in the Tavoliere, Southeastern Italy — A regional study". Journal of Archaeological Science: Reports. 20: 284–292. doi:10.1016/j.jasrep.2018.04.035. S2CID 134356403.
  40. ↑ A. M. Pollard; Carl Heron (2008). Archaeological Chemistry. Royal Society of Chemistry. ISBN 978-0854042623.
  41. ↑ Oates, J.; McMahon, A.; Karsgaard, P.; Quntar, S. A.; Ur, J. (2 January 2015). "Early Mesopotamian urbanism: a new view from the north" (PDF). Antiquity. 81 (313): 585–600. doi:10.1017/S0003598X00095600. S2CID 3803714.
  42. ↑ Tripković, Boban (2003). "The Quality and Value In Neolithic Europe: An Alternative View on Obsidian Artifacts". South Eastern Europe Proceedings of the ESF Workshop, Sofia. 103: 119–123. Retrieved 21 June 2019.
  43. 1 2 "John Dee's spirit mirror – The British Library". 2020-04-01. Archived from the original on 2020-04-01. Retrieved 2020-04-01.
  44. ↑ John Noble Wilford (2010-04-05). "In Syria, a Prologue for Cities". The New York Times.
  45. ↑ George Robert Rapp (2002). Archaeomineralogy. Springer. ISBN 978-3540425793.
  46. ↑ "Obsidian | Oki Islands UNESCO Global Geopark".
  47. ↑ Izuho, Masami; Sato, Hiroyumi (2007). "Archaeological obsidian studies in Hokkaido, Japan: Retrospect and prospects". Indo-Pacific Prehistory Association Bulletin. 27. doi:10.7152/bippa.v27i0.11982. Retrieved 2 March 2022.
  48. ↑ Yellin, Joseph; Levy, Thomas E.; Rowan, Yorke M. (1996). "New Evidence on Prehistoric Trade Routes: The Obsidian Evidence from Gilat, Israel". Journal of Field Archaeology. 23 (3): 361–68. doi:10.1179/009346996791973873.
  49. ↑ Brokmann, Carlos, Tipología y análisis de la obsidiana de Yaxchilán, Chiapas, Colección Científica, no. 422, INAH, 2000
  50. ↑ C. Michael Hogan (2008). Morro Creek, A. Burnham (ed.). Megalithic.co.uk. Retrieved on 2011-11-20.
  51. ↑ Panich, Lee; Michelini, Antonio; Shackley, M. (2012-12-01). "Obsidian Sources of Northern Baja California: The Known and the Unknown". Faculty Publications.
  52. ↑ Stark, Barbara L.; Boxt, Matthew A.; Gasco, Janine; González Lauck, Rebecca B.; Hedgepeth Balkin, Jessica D.; Joyce, Arthur A.; King, Stacie M.; Knight, Charles L. F.; Kruger, Robert (2016-03-01). "Economic growth in Mesoamerica: Obsidian consumption in the coastal lowlands". Journal of Anthropological Archaeology. 41: 263–282. doi:10.1016/j.jaa.2016.01.008. ISSN 0278-4165.
  53. ↑ Mario Pino Quivido & Rayen Navarro (2005). "Geoarqueología del sitio arcaico Chan-Chan 18, costa de Valdivia: Discriminación de ambientes de ocupación humana y su relación con la transgresión marina del Holoceno Medio". Revista Geológica de Chile. 32. doi:10.4067/S0716-02082005000100004.
  54. ↑ Naranjo, José A; Stern, Charles R (2004). "Holocene tephrochronology of the southernmost part (42°30'–45°S) of the Andean Southern Volcanic Zone". Revista Geológica de Chile. 31 (2): 225–40. doi:10.4067/S0716-02082004000200003. OCLC 61022562.
  55. ↑ Specht, Jim (2018). "Research issues in the circum-New Guinea islands". In Cochrane, Ethan E.; Hunt, Terry L. (eds.). The Oxford Handbook of Prehistoric Oceania. Oxford University Press. p. 100. ISBN 978-0-19-992507-0.
  56. ↑ Eric Kjellgren; JoAnne Van Tilburg; Adrienne Lois Kaeppler (2001). Splendid Isolation: Art of Easter Island. Metropolitan Museum of Art. pp. 39–. ISBN 978-1-58839-011-0.
  57. ↑ Shadbolt, Peter (2015-04-02). "CNN Health: How Stone Age blades are still cutting it in modern surgery". CNN. Retrieved 2023-09-07.
  58. 1 2 3 Buck, BA (March 1982). "Ancient Technology in Contemporary Surgery". The Western Journal of Medicine. 136 (3): 265–269. PMC 1273673. PMID 7046256.
  59. ↑ Haviland, W.A.; Prins H.E.L.; Walrath D.; McBride B. (2010). Anthropology: The Human Challenge (13 ed.). Cengage Learning. p. 196. ISBN 9780495810841. Retrieved 27 September 2012.
  60. ↑ Disa, J. J.; Vossoughi, J.; Goldberg, N. H. (October 1993). "A comparison of obsidian and surgical steel scalpel wound healing in rats". Plastic and Reconstructive Surgery. 92 (5): 884–887. doi:10.1097/00006534-199392050-00015. PMID 8415970.
  61. ↑ Fine Science Tools (FST). "FST product catalog". FST. Retrieved 7 September 2012.
  62. ↑ "Fine Science Tools - Obsidian Scalpels" https://www.finescience.com/en-US/Products/Scalpels-Blades/Micro-Knives/Obsidian-Scalpels
  63. ↑ Manutchehr-Danai, Mohsen (2013-03-09). Dictionary of Gems and Gemology. Springer Science & Business Media. ISBN 9783662042885.
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