Escala de Mohs

Escala de Mohs quantifica a dureza dos minerais, isto é, a resistência que um determinado mineral oferece ao risco, ou seja, à retirada de partículas da sua superfície.

O diamante risca o vidro, portanto, é mais duro que o vidro. Esta escala foi criada em 1812 pelo mineralogista alemão Friedrich Vilar Mohs com dez minerais de diferentes durezas existentes na crosta terrestre.

Atribuiu valores de 1 a 10. O valor de dureza 1 foi dado ao material menos duro da escala, que é o talco, e o valor 10 dado ao diamante que é a substância mais dura conhecida na natureza.

Esta escala não corresponde à dureza absoluta de um material. Por exemplo, o diamante tem dureza absoluta 1 500 vezes superior à do talco. Entre 1 e 9, a dureza aumenta de modo mais ou menos uniforme, mas de 9 para 10 há uma diferença muito acentuada, pois o diamante é muito mais duro que o coríndon (ou seja, que o rubi e a safira).[1]

Dureza Mineral Fórmula química Dureza absoluta Imagem
1 Talco (pode ser arranhado facilmente com a unha) Mg3Si4O10(OH)2 1
2 Gipsita (ou gesso) (pode ser arranhado com unha com um pouco mais de dificuldade) CaSO4·2H2O 3
3 Calcita (pode ser arranhado com uma moeda de cobre) CaCO3 9
4 Fluorita (pode ser arranhada com uma faca de cozinha) CaF2 21
5 Apatita (pode ser arranhada dificilmente com uma faca de cozinha) Ca5(PO4)3(OH-,Cl-,F-) 48
6 Feldspato / ortoclásio (pode ser arranhado com uma liga de aço) KAlSi3O8 72
7 Quartzo (capaz de arranhar o vidro. Ex.: ametista) SiO2 100
8 Topázio (capaz de arranhar o quartzo) Al2SiO4(OH-,F-)2 200
9 Corindon (capaz de arranhar o topázio. Exs.: safira e rubi) Al2O3 400
10 Diamante (mineral mais duro que existe, pode arranhar qualquer outro e é arranhado apenas por outro diamante) C 1 600

A escala de dureza Mohs é usada em mineralogia; no entanto, existem outras escalas de dureza utilizadas em ciência dos materiais, tais como:

Dureza intermediária

A tabela abaixo incorpora substâncias adicionais susceptíveis de serem abrangidas entre os níveis:

Dureza Substância ou mineral
0.2–0.3 césio, rubídio
0.5–0.6 lítio, sódio, potássio
1 talco
1.5 gálio, estrôncio, índio, estanho, bário, tálio, chumbo, grafite, gelo[2]
2 hexagonal nitreto de boro,[3] cálcio, selênio, cádmio, enxofre, telúrio, bismuto, gesso
2.5–3 ouro, prata, alumínio, zinco, lantânio, cério, azeviche
3 calcite, cobre, arsénico, antimônio, tório, dentina
3.5 platina
4 fluorite, ferro, níquel
4–4.5 aço
5 apatita (esmalte dentário), zircônio, paládio, obsidiana (vidro vulcânico)
5.5 berílio, molibdénio, háfnio, vidro, cobalto, magnetita
6 ortoclase, titânio, manganês, germânio, nióbio, ródio, urânio
6–7 quartzo fundido, pirita, silício, rutênio, irídio, tântalo, Opala, peridoto, tanzanite
7 ósmio, quartzo, rênio, Vanádio
7.5–8 esmeralda, aço temperado, tungstênio, espinela
8 topázio, zircônia cúbica
8.5 Crisoberilo, Crômio, Nitreto de silício, carbeto de tântalo
9 coríndon, carbeto de tungstênio
9–9.5 carboneto de silício (carborundum), carboneto de titânio
9.5–10 boro, nitreto de boro, Rhenium diboride, stishovite, diboreto de titânio
10 diamante, carbonado
>10 diamante nanocristalino (hyperdiamond, ultrahard fullerite)


Referências

  1. ↑ «Mohs hardness (mineralogy) -- Britannica Online Encyclopedia» (em inglês). Britannica.com. Consultado em 5 de janeiro de 2012 
  2. ↑ "Ice is a mineral" Arquivado em 30 de outubro de 2015, no Wayback Machine. in Exploring Ice in the Solar System. messenger-education.org
  3. ↑ Berger, Lev I. (1996). Semiconductor Materials First ed. Boca Raton, FL: CRC Press. p. 126. ISBN 978-0849389122 

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