Lodestone

The process by which lodestone is created has long been an open question in geology. Only a small amount of the magnetite on the Earth is found magnetized as lodestone. Ordinary magnetite is attracted to a magnetic field as iron and steel are, but does not tend to become magnetized itself; it has too low a magnetic coercivity, or resistance to magnetization or demagnetization.{{cite book

| last1 = Livingston

| first1 = James D.

| title = Driving Force: The Natural Magic of Magnets

| publisher = Harvard University Press

| date = 1996

| pages = 14–20

| url = https://books.google.com/books?id=Xc_v9KUQaugC&q=Lodestone+magnetite+maghemite&pg=PA17

| isbn = 0674216458

}} Microscopic examination of lodestones has found them to be made of magnetite (Fe₃O₄) with inclusions of maghemite (cubic Fe₂O₃), often with impurity metal ions of titanium, aluminium, and manganese.{{cite journal

|doi=10.1029/1999GL900496

|first=Peter

|last=Wasilewski

|author2=Günther Kletetschka

|title=Lodestone: Nature's only permanent magnet - What it is and how it gets charged

|journal=Geophysical Research Letters

|volume=26

|issue=15

|pages=2275–78

|year=1999

|bibcode = 1999GeoRL..26.2275W }}{{cite book

| last1 = Warner

| first1 = Terence E.

| title = Synthesis, Properties and Mineralogy of Important Inorganic Materials

| publisher = John Wiley and Sons

| date = 2012

| pages = 114–115

| url = https://books.google.com/books?id=IR_IxoBT_S4C&q=Lodestone+magnetite+maghemite&pg=PA114

| isbn = 978-0470976029

}} This inhomogeneous crystalline structure gives this variety of magnetite sufficient coercivity to remain magnetized and thus be a permanent magnet.

The other question is how lodestones get magnetized. The Earth's magnetic field at 0.5 gauss is too weak to magnetize a lodestone by itself. The leading theory is that lodestones are magnetized by the strong magnetic fields surrounding lightning bolts. This is supported by the observation that they are mostly found near the surface of the Earth, rather than buried at great depth.

One of the earliest known references to lodestone's magnetic properties was made by 6th century BC Greek philosopher Thales of Miletus,{{cite web | last = Brand | first = Mike | author2 = Sharon Neaves | author3 = Emily Smith | title = Lodestone | work = Museum of Electricity and Magnetism, Mag Lab U | publisher = US National High Magnetic Field Laboratory | year = 1995 | url = http://www.magnet.fsu.edu/education/tutorials/museum/lodestone.html | access-date = 2009-06-21 | archive-url = https://web.archive.org/web/20090501063207/http://www.magnet.fsu.edu/education/tutorials/museum/lodestone.html | archive-date = 2009-05-01 | url-status = dead }} whom the ancient Greeks credited with discovering lodestone's attraction to iron and other lodestones.{{cite book | last = Keithley | first = Joseph F. | title = The Story of Electrical and Magnetic Measurements: From 500 B.C. to the 1940s | publisher = John Wiley and Sons | year = 1999 | pages = 2 | url = https://books.google.com/books?id=uwgNAtqSHuQC | isbn = 0-7803-1193-0}} The name magnet may come from lodestones found in Magnesia, Anatolia.The Greek term μαγνῆτις λίθος magnētis lithos (see [https://archive.org/details/bub_gb_BkS2KW7u76MC Platonis Opera], Meyer and Zeller, 1839, p. 989) means "Magnesian stone". It is uncertain whether the adjective μαγνῆτις "of Magnesia" should be taken to refer to the city Magnesia ad Sipylum in Lydia (modern-day Manisa, Turkey) or after the Greek region of Magnesia itself (whence came the colonist who founded the Lydian city); see, for example, {{cite web|url=http://www.languagehat.com/archives/001914.php |title=Magnet |work=Language Hat blog |date=28 May 2005 |access-date = 22 March 2013}} See also: Paul Hewitt, Conceptual Physics. 10th ed. (2006), p. 458. The ancient Indian medical text Sushruta Samhita describes using magnetic properties of the lodestone to remove arrows embedded in a person's body.{{citation needed|date=July 2024}}

The earliest Chinese literary reference to magnetism occurs in the 4th-century BC Book of the Devil Valley Master (Guiguzi).The section "Fanying 2" (反應第二) of The Guiguzi: "{{lang|zh|其察言也，不失若磁石之取鍼，舌之取燔骨}}".

In the chronicle Lüshi Chunqiu, from the 2nd century BC, it is explicitly stated that "the lodestone makes iron come or it attracts it."{{Cite book |title=Encyclopedia of Chinese History |last= Dillon |first= Michael |publisher= Routledge |year=2017 |isbn=978-0415426992 |pages=98}}{{cite journal |last=Li |first=Shu-hua |title=Origine de la Boussole II. Aimant et Boussole |journal=Isis |volume=45 |number=2 |year=1954 |pages=175–196|jstor=227361|doi=10.1086/348315|s2cid=143585290 | quote = un passage dans le Liu-che-tch'ouen-ts'ieou [...]: “La pierre d'aimant fait venir le fer ou elle l'attire.” | language = fr}}
From the section "Jingtong" ({{lang|zh|精通}}) of the "Almanac of the Last Autumn Month" ({{lang|zh|季秋紀}}): "{{lang|zh|慈石召鐵，或引之也}}]" The earliest mention of a needle's attraction appears in a work composed between 20 and 100 AD, the Lunheng (Balanced Inquiries): "A lodestone attracts a needle."In the section "[https://archive.org/stream/lunheng02wang#page/350/mode/1up A Last Word on Dragons]" ({{lang|zh|亂龍篇}} Luanlong) of the Lunheng: "Amber takes up straws, and a load-stone attracts needles" ({{lang|zh|頓牟掇芥，磁石引針}}). In the 2nd century BC, Chinese geomancers were experimenting with the magnetic properties of lodestone to make a "south-pointing spoon" for divination. When it is placed on a smooth bronze plate, the spoon would invariably rotate to a north–south axis.{{Cite book |title=Echoes from Old China: Life, Legends, and Lore of the Middle Kingdom |last=Tom |first=K. S. |publisher=University of Hawaii Press |year=1989 |pages=108}}{{Cite book |title=Chinese Fans: Artistry and Aesthetics |last= Qian |first= Gonglin |publisher=Long River Press |year=2000 |isbn= 978-1592650200 |pages=98}}{{Cite book |title=The History of China: (The Greenwood Histories of the Modern Nations) |last=Curtis Wright |first=David |publisher=Greenwood Publishing Group |year=2001 |pages=42}} While this has been shown to work, archaeologists have yet to discover an actual spoon made of magnetite in a Han tomb.Joseph Needham, Clerks and Craftsmen in China and the West: Lectures and Addresses on the History of Science and Technology. Cambridge: University Press, 1970, p. 241.

Based on his discovery of an Olmec artifact (a shaped and grooved magnetic bar) in North America, astronomer John Carlson suggests that lodestone may have been used by the Olmec more than a thousand years prior to the Chinese discovery.{{cite journal|last1=Carlson|first1=J. B.|title=Lodestone Compass: Chinese or Olmec Primacy?: Multidisciplinary analysis of an Olmec hematite artifact from San Lorenzo, Veracruz, Mexico|journal=Science|volume=189|issue=4205|year=1975|pages=753–760|issn=0036-8075|doi=10.1126/science.189.4205.753|pmid=17777565|bibcode=1975Sci...189..753C|s2cid=33186517}} Carlson speculates that the Olmecs, for astrological or geomantic purposes, used similar artifacts as a directional device, or to orient their temples, the dwellings of the living, or the interments of the dead. Detailed analysis of the Olmec artifact revealed that the "bar" was composed of hematite with titanium lamellae of Fe_2–xTi_xO₃ that accounted for the anomalous remanent magnetism of the artifact.[http://deepblue.lib.umich.edu/bitstream/handle/2027.42/23074/0000648.pdf?sequence=1 Evans, B. J., Magnetism and Archaeology: Magnetic Oxides in the First American Civilization, p. 1097, Elsevier, Physica B+C 86-88 (1977), S. 1091-1099]

"A century of research has pushed back the first mention of the magnetic compass in Europe to Alexander Neckam about +1190, followed soon afterwards by Guyot de Provins in +1205 and Jacques de Vitry in +1269. All other European claims have been excluded by detailed study..."Needham, Clerks and Craftsmen, p. 240.

Lodestones have frequently been displayed as valuable or prestigious objects. The Ashmolean Museum in Oxford contains a lodestone adorned with a gilt coronet that was donated by Mary Cavendish in 1756, possibly to secure her husband's appointment as Chancellor of Oxford University.{{Cite web|url=https://mhs.web.ox.ac.uk/collections-online#/item/hsm-narrative-10530|title=Inv. 47759 - Sphaera article|last=Kell|first=Patricia|date=1996}} Isaac Newton's signet ring reportedly contained a lodestone which was capable of lifting more than 200 times its own weight.{{Cite book|url=http://www.bitnick.it/Fonti/Thompson%20-%20Electromagnet.pdf|title=The Electromagnet, and Electromagnetic Mechanism|last=Thompson|first=Sylvanus|publisher=E. & F. N. Spon|year=1891|location=London|pages=128}} And in 17th century London, the Royal Society displayed a {{convert|6|in|cm|adj=on}} spherical lodestone (a terrella or 'little Earth'), which was used to illustrate the Earth's magnetic fields and the function of mariners' compasses.{{Cite web|url=https://pictures.royalsociety.org/image-rs-8487|title=A terella|website=The Royal Society Picture Library}} One contemporary writer, the satirist Ned Ward, noted how the terrella "made a paper of Steel Filings prick up themselves one upon the back of another, that they stood pointing like the Bristles of a Hedge-Hog; and gave such Life and Merriment to a Parcel of Needles, that they danc'd [...] as if the devil were in them."{{Cite book|title=Sympathetic Attractions: Magnetic Practices, Beliefs, and Symbolism in Eighteenth-Century England|last=Fara|first=Patricia|publisher=Princeton University|year=1996|isbn=9780691634913|pages=23}}

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• [http://www.phy6.org/earthmag/lodeston.htm Lodestone]

Category:Ancient Greek technology

Category:Electric and magnetic fields in matter

Category:Iron(II,III) minerals

Category:Oxide minerals