[meteorite-list] Maskelynite - a repost

[bernd.pauli at paulinet.de]

Jeff from "Down Under" wrote:

> Can anyone tell me exactly how Maskelynite is
> formed and if it has been found on Earth?


Maskelynite

01) John G. Burke, Cosmic Debris, Meteorites in History, page 190:

In 1871 Tschermak wrote to Maskelyne: I am still continually busy with
meteorites, chiefly with an investigation of the Shergotty stone. I have
found therein an augite  and a colorless silicate that crystallizes in the
tesseral isometric system . I shall analyse the latter in the next few days.
It is probably something new, and I shall give it the name Maskelynite, in 
your honor since you were the first to have undertaken the analyses of
meteoritic minerals in the most salutary way.

page 191: Tschermak's initial judgment concerning maskelynite was
somewhat off the mark; it is a plagioclase , labradorite , converted
by a preterrestrial impact shock to an isotropic or imperfectly isotropic
glass.

page 244: Shock has been shown to be the cause of the transformation
of a normal plagioclase feldspar into the mineral maskelynite.

=> maskelynite = plagioclase feldspar transformed by intense
   shock pressure plagioclase feldspar = (Na,Ca)(SiAl)3O8

02) J.T. Wasson, Meteorites, pp. 73-74:

Investigations during the past few years show that many common petrological
features of meteorites are of shock origin ... Some of these properties are
produced only by shock (e.g. Neumann lamellae or maskelynite), whereas others
are purely thermal effects.

Shock indicator	*Minimum* shock pressure (kb) 
Plagioclase > maskelynite	      300
Neumann lamellae in kamacite	10


Best wishes,

Bernd