A lodestone or loadstone is a naturally magnetized piece of the mineral magnetite. They are permanent and naturally occurring magnets, that attract pieces of iron. Ancient people first discovered the property of magnetism in lodestone.[1] Pieces of lodestone, suspended so they could turn, were the first magnetic compasses,[1][2][3][4] and their importance to early navigation is indicated by the name lodestone, which in Middle English means 'course stone' or 'leading stone'.[5] Lodestone is one of only two minerals that is found naturally magnetized; the other, pyrrhotite, is only weakly magnetic.[6] It is black or brownish-black with a metallic luster, has a hardness of 5.5-6.5 and a black streak.
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Origin
The process by which lodestone is created has long been an open question in geology. Only a small amount of the magnetite on Earth is found magnetized as lodestone. Ordinary magnetite is attracted to a magnetic field like iron and steel is, but does not tend to become magnetized itself. Recent research[7] has found that only a variety of magnetite with a particular crystalline structure, a mixture of magnetite and maghemite, has sufficient coercivity to be magnetized and become a permanent magnet. One theory suggests that lodestones are magnetized by the strong magnetic fields surrounding lightning bolts.[7] This is supported by the observation that they are mostly found at the surface of the Earth; not buried at great depth.
History
One of the first references to lodestone's magnetic properties is by 6th century BCE Greek philosopher Thales of Miletus[8] who is credited by the ancient Greeks with discovering lodestone's attraction to iron and other lodestones.[9] The name "magnet" may come from lodestones found in Magnesia, a portion of ancient Thessaly, Greece[10]. In China, the earliest literary reference to magnetism lies in a 4th century BCE book called Book of the Devil Valley Master (鬼谷子): "The lodestone makes iron come or it attracts it."[11] The earliest mention of the attraction of a needle appears in a work composed between 20 and 100 CE (Louen-heng): "A lodestone attracts a needle."[11] The lodestone compass was used for navigation in Europe and China by the 12th century.[citation needed]
References
- ^ a b Du Trémolet de Lacheisserie, Étienne; Damien Gignoux, Michel Schlenker (2005). Magnetism: Fundamentals. Springer. pp. 3–6. ISBN 0387229671. http://books.google.com/books?id=MgCExarQD08C&pg=PA3.
- ^ Dill, J. Gregory (Jan/Feb 2003). "Lodestone and Needle: The rise of the magnetic compass". Ocean Navigator online. Navigator Publishing. https://oceannavigator.com/ME2/dirmod.asp?sid=&nm=&type=Publishing&mod=Publications%3A%3AArticle&mid=8F3A7027421841978F18BE895F87F791&tier=4&id=BA0BDFC75ACC44349A54E748F490EF45. Retrieved 2009-06-12.
- ^ Merrill, Ronald T.; Michael W. McElhinny, Phillip L. McFadden (1998). The Magnetic Field of the Earth. Academic Press. pp. 3. ISBN 012491246X. http://books.google.com/books?id=96APl4nK9lIC&pg=PA1&lpg=PA1&dq=lodestone+magnetic+compass&source=bl&ots=O4bYv3R61o&sig=t0yGuHrbCXEHYJMeDJFiUB7hR0w&hl=en&ei=8lsvSoL1L6fmtgPtgbXECA&sa=X&oi=book_result&ct=result&resnum=1#PPA3,M1.
- ^ Needham, Joseph; Colin A. Ronan (1986). The Shorter Science and Civilization in China. UK: Cambridge Univ. Press. pp. 6, 18. ISBN 0521315603. http://books.google.com/books?id=CjRAiqGSJ50C&pg=PA6.
- ^ "Lodestone". Mirriam-Webster online dictionary. Mirriam-Webster, Inc.. 2009. http://www.merriam-webster.com/dictionary/lodestone. Retrieved 2009-06-12.
- ^ Hurlbut, Cornelius Searle; W. Edwin Sharp, Edward Salisbury Dana (1998). Dana's minerals and how to study them. John Wiley and Sons. pp. 96. ISBN 0471156779. http://www.google.com/books?id=pgn5w0JPWlMC&pg=PA84&dq=lodestone+pyrrhotite.
- ^ a b Wasilewski, Peter; Günther Kletetschka (1999). "Lodestone: Nature's only permanent magnet - What it is and how it gets charged". Geophysical Research Letters 26 (15): 2275–78. http://lep694.gsfc.nasa.gov/gunther/gunther/Wasilewski1999.pdf. Retrieved 2009-07-13.
- ^ Brand, Mike; Sharon Neaves, Emily Smith (1995). "Lodestone". Museum of Electricity and Magnetism, Mag Lab U. US National High Magnetic Field Laboratory. http://www.magnet.fsu.edu/education/tutorials/museum/lodestone.html. Retrieved 2009-06-21.
- ^ Keithley, Joseph F. (1999). The Story of Electrical and Magnetic Measurements: From 500 B.C. to the 1940s. John Wiley and Sons. pp. 2. ISBN 0780311930. http://books.google.com/books?id=uwgNAtqSHuQC.
- ^ Paul Hewitt, "Conceptual Physics". 10th ed. (2006), p.458
- ^ a b Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” Isis, Vol. 45, No. 2. (Jul., 1954), p.175
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