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1. A metallic mixture, once considered an element, composed of neodymium and praseodymium.
2. A mixture of rare-earth elements and their oxides used chiefly in manufacturing and in coloring various forms of glass.

[From Greek didumos, twin, double (from the fact that it was usually found associated with the previously discovered lanthanum ); see dwo- in Indo-European roots.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(daɪˈdɪmɪəm; dɪ-)
1. (Elements & Compounds) a mixture of the metallic rare earths neodymium and praseodymium, once thought to be an element
2. (Elements & Compounds) a mixture of rare earths and their oxides used in colouring glass
3. (Colours) a mixture of rare earths and their oxides used in colouring glass
[C19: from New Latin, from Greek didumos twin + -ium]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(daɪˈdɪm i əm, dɪ-)

a mixture of neodymium and praseodymium formerly thought to be an element. Symbol: Di
[< Greek dídym(os) twin (see didymous) + New Latin -ium -ium2; so named by Swedish chemist Carl Mosander (1797–1858), who discovered it in 1843, from its close association with lanthanum]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
References in periodicals archive ?
Didymium species correspond to almost 50% of the floricolous myxomycetes recorded in Costa Rica, Puerto Rico and Ecuador; however, the three species of the Didymiaceae family recorded in the present study were classified as occasional or scarce.
Crystallization and spherulitic growth of gadolinium, praseodymium, and mixed didymium heptamolybdate in silica gel medium [17, 18] have been investigated by many workers.
These elements are not only used in high-technology products; for example, didymium (a mixture of praseodymium and neodymium) has been used for over a century to color safety glass for glassblowing and blacksmithing.
A high purity didymium oxide (a neodymium - praseodymium mix) sample is expected in June, followed by cerium oxide and finally a lanthanum oxide.
Molycorp Inc (NYSE:MCP), producer of rare earth oxides (REO), has reached a three-year agreement with Hitachi Metals for an undisclosed amount whereby Hitachi will supply Molycorp with rare earth magnetic materials including Didymium (a mix of neodymium and praseodymium) metal and alloy and Lanthanum Oxide, it declared on Friday.
It is estimated that 2,500 tons of cerium and lanthanum-based products and 250 tons of didymium would start shipping to Japan around February 2011, making it the first major rare earth shipment to Japan from non-Chinese sources.
Molycorp is expected to provide Sumitomo with approximately 2,500 metric tons per year of cerium- and lanthanum-based products and 250 metric tons of didymium oxide (a combination of neodymium and praseodymium) per year from its current production facility at Mountain Pass, California.
The plant will produce 800 tons a year in total of didymium and dysprosium metals, which are used as raw material for neodymium-based high-performance magnetic alloys.
Wavelength accuracy over the UV-visible range should be checked routinely with the aid of NIST-traceable holmium, erbium, or didymium oxide filters, using the working instrument resolution.
He named this new element didymium (Greek for "twin") because, as he said, it seemed to be "an inseparable twin brother of lanthanum" (Weeks, 1968).