Tui or Parson Bird Prosthemadera Novae Zealandiae. From: 'A history of the birds of New Zealand' by Walter Lawry Buller
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Hand-drawn diagrams of the polymorphs of silica

Files

Date

c. 1935

Identifier

Mellor Papers

Type

Publisher

Unpublished

Abstract

This diagram shows the basic tetrahedral SiO4 building block (Fig. 51) and α-quartz (Fig. 235), β-quartz (Fig. 236), β-cristobalite (Fig. 236) and β-tridymite (Fig. 237). Polymorphs have the same chemical formulae but different structures. Mellor describes the significance of these forms in the glazing process. 'Nature has set limits of temperature within which each form of silica is stable. If these limits be exceeded, the silica becomes unstable and undergoes a molecular cataclysm, whereby the structural units rearrange themselves of their own accord, slowly or quickly, according to a different architectural plan, so as to produce another kind of silica which is stable only in a new range of temperature' (Mellor, Crazing and Peeling of Glazes, 1935).

Citation

Joseph W. Mellor, “Hand-drawn diagrams of the polymorphs of silica,” ourheritage.ac.nz | OUR Heritage, accessed August 15, 2018, http://otago.ourheritage.ac.nz/items/show/9008.

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