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KNOOP HARDNESS NUMBERS FOR 127 OPAQUE MINERALS

1961; Geological Society of America; Volume: 72; Issue: 4 Linguagem: Inglês

10.1130/0016-7606(1961)72[621

1943-2674

Forbes Smith Robertson,

Geological and Geochemical Analysis

Research Article| April 01, 1961 KNOOP HARDNESS NUMBERS FOR 127 OPAQUE MINERALS FORBES ROBERTSON FORBES ROBERTSON THE PRINCIPIA COLLEGE, ELSAH, ILLINOIS Search for other works by this author on: GSW Google Scholar GSA Bulletin (1961) 72 (4): 621–637. https://doi.org/10.1130/0016-7606(1961)72[621:KHNFOM]2.0.CO;2 Article history received: 04 Aug 1959 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation FORBES ROBERTSON; KNOOP HARDNESS NUMBERS FOR 127 OPAQUE MINERALS. GSA Bulletin 1961;; 72 (4): 621–637. doi: https://doi.org/10.1130/0016-7606(1961)72[621:KHNFOM]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Knoop indentation hardness numbers may be obtained on polished mineral grains as small as 10 microns in diameter. This paper gives average Knoop numbers for 127 opaque minerals and quartz. The limits of tests and the average hardness number are plotted on a logarithmic scale on which the lines representing the hardness range for a given mineral are reasonably comparable throughout the range from 1 to 1500.Bismuth (0.7) is the softest mineral tested, berthierite (1140) the hardest. Other representative hardnesses (Talmage-scale equivalents in parentheses) are: argentite, 26 (A); galena, 75 (B); chalcopyrite, 175 (C: tetrahedrite, 299 (D); niccolite, 460 (E); magnetite, 528 (F); ilmenite, 965 (G). Quartz, 467 (7 on the Mohs scale), is approximately equivalent on the Knoop scale to niccolite, 460 (5–5½ on the Mohs scale), and goethite, 476 (5–5½ on the Mohs scale), and softer than magnetite, 536 (5½–6½ on the Mohs scale).Some minerals exhibit striking differences in hardness in different crystallographic orientations. Molybdenite has a hardness of 12 parallel to {0001} cleavage and 60 at right angles to the cleavage; hucbnerite is 313 parallel to {010} cleavage and 463 at right angles to cleavage; enargite is 154 parallel to {110} cleavage and 378 at right angles to cleavage. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.