Afwillite is a calcium hydroxide nesosilicate mineral with formula Ca3Si2O4(OH)6. It occurs as glassy, colorless to white prismatic monoclinic crystals. Its Mohs scale hardness is 4.5. It occurs as an alteration mineral in contact metamorphism of limestone.

It was first described in 1925 for an occurrence in the Dutoitspan Mine, Kimberley, South Africa and was named for Alpheus Fuller Williams (1874-1953), a past official of the De Beers diamond company.

Afwillite is typically found in veins of spurrite and it belongs to the nesosilicate sub-class. It is monoclinic, its space group is P2 and its point group is 2.

Formation of afwillite

It is suggested that afwillite forms in fractured veins of the mineral spurrite. Jennite, afwillite, oyelite and calcite are all minerals that form in layers within spurrite veins. It appears that the afwillite, as well as the calcite, forms from precipitated fluids. The jennite is actually an alteration of the afwillite, but both formed from calcium silicates through hydration. Laboratory studies determined that afwillite forms at a temperature below 200°C, usually around 100°C.Kusachi, I, Henmi, C. And Henmi K. (1989) Afwillite and jennite from Fuka, Okayama Prefecture. Japan. Miner J. 14, 279-292.] Afwillite and spurrite are formed through contact metamorphism of limestone.Barthemy, D. (2000) Afwillite Mineral Data, (] Contact metamorphism is caused by the interaction of rock with heat and/or fluids from a nearby crystallizing silicate magma.Klein, C. and Dutrow, K. (2007) Manual of Mineral Science. 23rd Edition, 63, 596]

=Structure and properties= Afwillite has a complex monoclinic structure, and the silicon tetrahedra in the crystal structure are held together by hydrogen bonds.Malik, K. M. A & Jeffery J. W. (1976) A Re-investigation of the Structure of Afwillite. Acta Cryst. B32, 475] It has perfect cleavage parallel to its (101) and poor cleavage parallel to its (100) faces.Megaw H. D. (1952). The structure of Afwilltie. Acta Cryst. 5, 477] It is biaxial and its 2V angle, the measurement from one optical axis to the other optical axis, is 50 – 56 degrees. When viewed under crossed polarizers in a petrographic microscope, it displays first-order orange colors, giving a maximum birefringence of 0.0167 (determined by using the Michel- Levy chart). Afwillite is optically positive. Additionally, it has a prismatic crystal habit. Under a microscope afwillite looks like wollastonite, which is in the same family as afwillite.

Awfillite is composed of double chains that consist of calcium and silicon polyhedral connected to each other by sharing corners and edges. This causes continuous sheets to form parallel to its miller index [-101] faces. The sheets are bonded together by hydrogen bonds and are all connected by Ca-Si-O bonds (Malik and Jeffery 1976). Each calcium atom is in 6-fold octahedral coordination with the oxygen, and the silicon is in 4-fold tetrahedral coordination around the oxygen. Around each silicon there is one OH group and there are three oxygens that neighbor them. The silicon tetrahedra are arranged so that they share an edge with calcium(1), and silicon(2) shares edges with the calcium(2) and calcium(3) polyhedral. The silicon tetrahedra are held together by the OH group and hydrogen bonding occurs between the hydrogen in the OH and the silicon tetrahedra. Hydrogen bonding is caused because the positive ion, hydrogen, is attracted to negatively charge ions which, in this case, are the silicon tetrahedra.

Occurrence in concrete

Afwillite is one of the calcium silicates that form when Portland cement sets to form concrete. [ Moody, K. M., 1952, "The thermal decomposition of afwillite," The Mineralogical Society ] The cement gets its strength from the hydration of its di- and tri- calcium silicates.


External links

* [ Mindat with location data]
* [ Webmineral data]
* [ American Mineralogist PDF]

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • afwillite — afvilitas statusas T sritis chemija apibrėžtis Mineralas. formulė Ca₃[SiO₃OH]₂·2H₂O atitikmenys: angl. afwillite rus. афвиллит …   Chemijos terminų aiškinamasis žodynas

  • afwillite — noun A calcium hydroxide nesosilicate mineral, occurring as glassy, colourless to white prismatic monoclinic crystals …   Wiktionary

  • afwillite — af·wil·lite …   English syllables

  • afwillite — ˈafwə̇ˌlīt noun ( s) Etymology: Alpheus Fuller Williams b1874 American mining engineer + English ite : a mineral Ca3Si2O4(OH)6 consisting of a hydrous calcium silicate and occurring in colorless monoclinic crysta …   Useful english dictionary

  • Bultfonteinite — Catégorie IX : silicates[1] Bultfonteinite, Wessels Mine, Afrique du Sud, 7.6 x 6.5 x 3.9 cm …   Wikipédia en Français

  • List of minerals A-B (complete) — It is currently not possible to have a complete list of minerals . The International Mineralogical Association is the international group that recognises new minerals and new mineral names, however minerals discovered before 1959 did not go… …   Wikipedia

  • Spurrite — Infobox mineral name = Spurrite category = Silicate/carbonate mineral boxwidth = boxbgcolor = caption = Spurrite from New mexico formula = Ca5(SiO4)2CO3 molweight = color = Gray, gray white to lilac gray habit = Massive to granular system =… …   Wikipedia

  • List of minerals — This is a List of minerals for which there are Wikipedia articles. Mineral variety names and mineraloids are to be listed after the valid minerals for each letter.For a complete listing (about 4,000) of all mineral names: List of minerals… …   Wikipedia

  • Thaumasite — (white) with prehnite (green) from Fairfax Quarry, Virginia …   Wikipedia

  • Chalkomorphit — Ettringite Ettringite Catégorie VII : sulfates, sélénates tellurates, chromates, molybdates, tungstates Ettringite Mines de N Chwaning, Afrique du Sud (6.5x3.2 cm) …   Wikipédia en Français

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.