[meteorite-list] More on Chladnite (Was: Rocks from Space Picture of the Day - August 24, 2010) - Part 2

From: bernd.pauli at paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: 24 Aug 2010 16:56:30 UT
Message-ID: <DIIE.0000004300004F6E_at_paulinet.de>

BURKE J.G. (1986) Cosmic Debris, Meteorites in History, Chapter 4, p. 121:

Chladnite:

Again, it was an observation by Charles U. Shepard that paved the way toward the
identification of the pyroxenes. In 1846 he described a mineral which, he wrote,
"is a ter-silicate of magnesia...[and] forms more than two-thirds of the Bishopville
stone". He named the mineral chladnite "in honor of Chladni, the scientific founder
of this department of knowledge." Two years later Shepard reported his analytical
results: 70 percent silicic acid, 28 percent magnesia, and 1 percent soda, so that the
ratio of oxygen in the magnesia to that in the silica was 1 to 3. In 1851 Sartorius von
Waltershausen analyzed a fragment of the Bishopville meteorite and arrived at about
the same results, but also found 1.5 percent alumina. Though making errors in his
calculations, Sartorius did produce the correct formula - MgO,SiO2; however, he
postulated that chladnite was a kind of wollastonite, in which magnesia substituted
for lime. The issue was confused further in 1861, when Rammelsberg found by
analysis almost 3 percent alumina, 35 percent magnesia, and only 57.5 percent silicic
acid. Doubting the existence of a definite mineral, Rammelsberg did not attempt to
devise a chemical formula.

Meanwhile, Shepard in 1854 described the Tucson iron meteorite and speculated
that certain inclusions were chladnite. J. Lawrence Smith immediately corrected
him, pointing out that the inclusions were actually olivine, and added a note that
he suspected "chladnite is likely to prove a pyroxene". At about the same time, in
1855, Gustav A. Kenngott, professor of mineralogy at Zurich, published a memoir
giving details of the minerals of what he termed the "augite group" of the pyroxenes.
One member of the group was enstatite, which, Kenngott wrote, was a bisilicate of
magnesia, was "augitic in crystallization," and had the formula 3MgO,2SiO3.
In 1861, when Kenngott saw Rammelsberg's analysis of chladnite, he insisted that
the mineral was identical with enstatite. Smith then made two analyses of the
Bishopville meteorite and reported in 1864 that chladnite consisted of 60 percent
silica and nearly 40 percent magnesia. He agreed with Kenngott that the mineral
was the magnesian pyroxene, enstatite, and accepted Kenngott's formula, in which
the oxygen content of the magnesia to that of the silica was 1 to 2. Both Rammelsberg
and Maskelyne acted to clarify the formula of enstatite, and through his work on the
Breitenbach, Bustee, and Manegaon meteorites, Maskelyne recognized the existence
of solid-solution series that included enstatite and bronzite. By the 1870s mineralogists
began to report regularly these constituents in meteorites.
Received on Tue 24 Aug 2010 12:56:30 PM PDT