Lodestone
A lodestone or loadstone is a naturally magnetized piece of the mineral magnetite. They are 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] Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5.5-6.5 and a black streak.
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 remain magnetized and thus be 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.[10]. In China, the earliest literary reference to magnetism lies in a 4th century BC 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 A.C. (Louen-heng): "A lodestone attracts a needle."[11] The lodestone compass was used for navigation in medieval China by the 12th century. This compass slowly made its way to Europe, and with this new technology, and many others, sparked the age of exploration in Europe.[citation needed]
References
- ^ a b Du Trémolet de Lacheisserie, Étienne (2005). Magnetism: Fundamentals. Springer. pp. 3–6. ISBN 0387229671.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Dill, J. Gregory (Jan/Feb 2003). "Lodestone and Needle: The rise of the magnetic compass". Ocean Navigator online. Navigator Publishing. Retrieved 2009-06-12.
{{cite web}}: Check date values in:|date=(help); Cite has empty unknown parameter:|coauthors=(help) - ^ Merrill, Ronald T. (1998). The Magnetic Field of the Earth. Academic Press. p. 3. ISBN 012491246X.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Needham, Joseph (1986). The Shorter Science and Civilization in China. UK: Cambridge Univ. Press. pp. 6, 18. ISBN 0521315603.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ "Lodestone". Mirriam-Webster online dictionary. Mirriam-Webster, Inc. 2009. Retrieved 2009-06-12.
- ^ Hurlbut, Cornelius Searle (1998). Dana's minerals and how to study them. John Wiley and Sons. p. 96. ISBN 0471156779.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ a b Wasilewski, Peter (1999). "Lodestone: Nature's only permanent magnet - What it is and how it gets charged" (PDF). Geophysical Research Letters. 26 (15): 2275–78. Retrieved 2009-07-13.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Brand, Mike (1995). "Lodestone". Museum of Electricity and Magnetism, Mag Lab U. US National High Magnetic Field Laboratory. Retrieved 2009-06-21.
{{cite web}}: External link in|publisher=|coauthors=ignored (|author=suggested) (help) - ^ Keithley, Joseph F. (1999). The Story of Electrical and Magnetic Measurements: From 500 B.C. to the 1940s. John Wiley and Sons. p. 2. ISBN 0780311930.
{{cite book}}: Cite has empty unknown parameter:|coauthors=(help) - ^ 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
External links
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