Apophyllite from Mexico

a small study in Mineral Identification

Mexican apophyllite [213 kb]

Above: a large sample of white tabular apophyllite with associated base-metal sulphides. Sample from Irwin Kennedy collection. This is the largest (by far) of three samples from the same locality. The smallest piece, a clear tabular crystal, was subjected to non-destructive testing, leading to the mineral identification and some additional understanding of the mineral occurrence. The three samples, dominated by the same tabular, white to colourless mineral are from Mina Cobresas at La Paz, on the east flank of the Sierra de Catorce, west of the city of Matehuala, which is in the northern tip of the state of San Luis Potosi, 70 km northeast of Charcas.

"Rock of the Month #134, posted for August 2012" ---

Apophyllite is a potassium-calcium silicate mineral. A tetragonal phase, it has an unusual structure with sheets of (Si-O) tetrahedra arranged into 4-fold and 8-fold rings, sandwiching layers containing the other constituent atoms and molecules (K, Ca, F and H2O). The perfect cleavage along the sheet structure imparts a pearly lustre, in contrast to prism faces, which are vitreous. The habit is also variable, and includes prisms, blunt pseudocubic crystals, and flattened, tabular forms. See Deer et al. (2009) for a modern technical description.

It occurs as a secondary mineral lining and infilling amygdales in basaltic lava flows, often in association with zeolites (although it is NOT a zeolite), and is also found in contact metamorphic environments. Skarns such as Dal'negorsk (Grant and Wilson, 2001) and Broadford (on the island of Skye in northwest Scotland: Tilley, 1951) are well-known. The occurrences with zeolites in the Deccan Traps of western India (around Poona in the state of Maharashtra) are especially celebrated, and well-documented (e.g., Jeffery et al., 1988; Ottens, 2003; Kothavala, 2003; Makki and Makki, 2008; Wilson, 2009).

Further Information

A more detailed description and discussion of the samples and their identification will be found here, as a 410-kb pdf file, together with photos of the two smaller samples. Five I.K. apophyllite samples, including the mid-size (63-g) mass examined here, were viewed and their specific gravity determined in November 2012. The calculated specific gravity of apophyllite is circa 2.36-2.37. The visually-purest sample, from Carazinho, Rio Grande do Sul, Brazil, collected in 1970, yields a measurement of 2.36. The sample is a 92-g aggregate of fine, pale greenish to colourless tetragonal prisms. The other samples gave lower values, including 2.27 for the 63-g Mina Cobresas specimen, which is partially invested with impurities. Measured values of S.G. for apophyllite are commonly quoted as 2.33-2.37.


Deer,WA, Howie,RA and Zussman,J (editors) (2009) Rock Forming Minerals, Volume 3B: Layered Silicates Excluding Micas and Clay Minerals (second edition). Geological Society Publishing House, 314pp.

Grant,R and Wilson,WE (2001) Dal'negorsk: Primorskiy Kray, Russia. Mineral.Record 32 no.1, 3-30.

Jeffery,KL, Henderson,P, Subbarao,KV and Walsh,JN (1988) The zeolites of the Deccan basalt - a study of their distribution. In `Deccan Flood Basalts' (Subbarao,KV editor), Geol.Soc.India Memoir 10, 393pp., 151-162.

Kothavala,RZ (2003) Recollections of mineral collecting and dealing in India. Mineral.Record 34, 135-154.

Makki,S and Makki,MF (2008) Green apophyllite from Bidkin, Aurangabad, India. Mineral.Record 39, 267-273.

Ottens,B (2003) Minerals of the Deccan Traps, India. Mineral.Record 34, 1-82.

Tilley,CE (1951) The zoned contact-skarns of the Broadford area, Skye: a study of boron-fluorine metasomatism in dolomites. Mineral.Mag. 29, 621-666.

Wilson,WE (editor) (2009) Private Mineral Collections in Texas. Mineral.Record 40 no.1, supplement, 180pp.


Natural History Museum, London, England, 13 November 2012.

The systematic mineralogy exhibit in this wonderful institution has been a favourite of mine since my first decade of mineral appreciation! Apophyllite is well represented. At the time of this visit there were some 30 pieces in the systematic case and six large display pieces in an end case. Examples include: white tabular crystals on quartz from Thul Ghat, India; lovely clear crystals on bluish quartz from Bombay, Maharashtra; a variety named ichthyophthalmite is composed of clear platy crystals with diopside and magnetite, from Uto in Sweden; a large greenish-white crystal with pink stilbite and silky white laumontite, from the Western Ghats; a crust of tabular crystals from the Jagersfontein mine in South Africa; and apophyllite of pseudocubic habit with quartz and chlorite, from Burger's quarry, New Jersey. The six display samples include: pearly white crystals of tetragonal form from Guanajuato in central Mexico; lovely pale green crystals in brownish-cream stilbite from San Pedrino, Rio Grande do Sul, Brazil; and two samples from the Siahadri Mountains near Bombay: a) pale brown with pink stilbite and b) a coarse crust on basalt comprising colourless, tabular apophyllite with pink stilbite. At a glance, the Thul Ghat and Jagersfontein crystals most reminded me of the tabular material from Mexico featured in this Rock of the Month.

Graham Wilson, posted 16 July 2012, extended 08 August 2012, upgraded with Museum Moment on 24 November 2012, 25 November 2012

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