In geology, what is a perimorph
? Allsopp interview in 2012?
One specimen found at the Huanzala mine shows a hollow calcite perimorph about 1.5 cm across with patches of corroded galena on its inner surface.
One very interesting specimen found in the Morococha district in January 2004 is a matrix entirely covered by a white crust of tiny quartz crystals, a perimorph after a crust of cuboctahedral crystals to about 1 cm.
It is a quartz perimorph after platy rectangular crystals, probably of barite.
One of the mines produced a quartz perimorph specimen showing a very thin quartz crust over a vanished 1.5-cm calcite rhombohedron.
Perimorphs of phillipsite-Ca after gi-smondine or clay mineral (saponite?) encrusting gismodine are rare.
Pseudomorphs and perimorphs of clay minerals after gismondine were also reported from basa-nites of Groft Teichelberg, Bavaria, by Pollmann and Keck (1990).Two generations of "clay minerals" (a post-phillipsite phase crystallizing instead of chabazi-te) were mentioned also by Tschernich (1992) in an assemblage with a general succession of zeolite crystallization controlled by a decrease in Si content (Si/Al ratio).
Perimorphs and pseudomorphs of clay minerals after gis-mondine, phillipsite-Ca and natrolite have been often reported (cf.
Perimorphs after calcite consisting of thin, dull white shells of gibbsite, fluorite and rarely doyleite, have been observed.
Perimorphs after cryolite have been found in both the upper and lower sills.
Admixed with gibbsite, doyleite commonly forms thin, shell-like perimorphs after cryolite from which the original cryolite has been partially or completely leached out.
In places it covers or replaces carbonates to form perimorphs