We have studied a small, very unusual stone, here named 鈥淗ypatia鈥? found in the area of southwest Egypt where an extreme surfa
ce heating event produ
ced the Libyan Desert Glass 28.5 million years ago. It is angular, bla
ck, shiny, extremely hard and intensely fra
ctured. We report on exploratory work in
cluding X-ray diffra
ction, Raman spe
ctros
copy, transmission ele
ctron mi
cros
copy, s
canning ele
ctron mi
cros
copy with EDS analysis, deuteron nu
clear rea
ction analysis, C-isotope and noble gas analyses. Carbon is the dominant element in Hypatia, with heterogeneous O/C and N/C ratios ranging from 0.3 to 0.5 and from 0.007 to 0.02, respe
ctively. The major
cations of sili
cates add up to less than 5%. The stone
consists
chiefly of apparently amorphous, but very hard
carbona
ceous matter, in whi
ch pat
ches of sub- diamonds o
ccur. values (
ca. 0鈥? ex
clude an origin from sho
cked terrestrial
coal or any variety of terrestrial diamond. They are also higher than the values for
carbona
ceous
chondrites but fall within the wide range for interplanetary dust parti
cles and
comet 81P/Wild2 dust. In step heating,
40Ar/
36Ar ratios vary from 40 to the air value (298), interpreted as a variable mixture of extraterrestrial and atmospheri
c Ar. Isotope data of Ne, Kr and Xe reveal the exoti
c noble gas
components
G and
P3 that are normally hosted in presolar SiC and nanodiamonds, while the most
common trapped noble gas
component of
chondriti
c meteorites,
Q, appears to be absent. An origin remote from the asteroid belt
can a
ccount for these features.
We propose that the Hypatia stone is a remnant of a cometary nucleus fragment that impacted after incorporating gases from the atmosphere. Its co-occurrence with Libyan Desert Glass suggests that this fragment could have been part of a bolide that broke up and exploded in the airburst that formed the Glass. Its extraordinary preservation would be due to its shock-transformation into a weathering-resistant assemblage.