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187
breccia was lisa observed, composed of anguw fragmentS of Krpmline.
lIll1ividWlI
serpentine grains••nd serpentine bmxia. :nay conuin sclnef"Cd opaque n1i~rab.
probably magnetite or chromilt.
An attempt was made 10 confirm ,he OOlal idc:nlirlC':lIion "r kl'Jl"ntine gr.ains
using electron microprobe analyses. This proved unsuccessful. partly ba:ausc: I~ soft
centres of lhe grains were removed by the polishing process. but mostly bo:t.:auk in all
cases grains optically idcI11ifi«l u serpentine IU~ oct to be composed of,hloTite:. The
variation in hardness from the interior to tho: cXler!or of the grains suggests lh~l a
chemical reaction his taken place which has altered the grain edgc:'I more than the
interiors (see r!ates 4.9.4.10). This could have: occurred while the: serpentine grain was
in the area where il was originally eroded. or il cook! have: occunnl as a diagenetic
rnclion wilhin!he Goose Tickle: group and Lower Head Formation. 1ne hypolhesis 1h:l1
composition varies from the CC:NreS of me grains 10 the edges is supported by probe
a:naIysn and subsequent qualitative: investigations usinglhe SEM, whk:h demonsU111al
thai the edges of me Brains are genenlly richer in aluminiuJTI ard iron relalive 10
magnesium. in c~rison with !be interiors of the graiN ".vhich are richer in magnesium
relalive:oaluminium,
~encefonhme graiN of serpenrine will be referred 10 as 'thlorilised serpenline',
Chlori!ised serpenrines in boIh the Goose Tickle group and the Lower Head Fonnalton
contain small bur significanr proponions of Cr and Ni (appendix 3, s«lions A3.l aoo
A3,3).
Grains from rnc Goose Tickle group show the highesl values of Cr anti Ni.
Typically, Cr and Ni are rarely analysed in chlorilCs which arc not indepcooenily known