There seems to be some confusion between Pietersite, crocidolite,
tigerseye, blue-black tigereye, falconseye and hawkseye.
The following is an extract describing Pietersite which would
indicate it is not a brecciated crocidolite as its only affinity with
that mineral is silica (jasper) and asbestos but has been formed in a
quite different manner.
Pietersite crystallises in the form of masses, the structure a result
of inclusions in jasper where the inclusions are pseudomorphs after
asbestos. The colour is blue/black and the mineral exhibits a
chatoyant quality. It was discovered by Sid Pieters, Windhoek,
Namibia, and is truly lovely.
Re the blue-black tigereye (crocidolite) it is apparent that this is
generally named 'hawkeye' in the USA, however in Minerals Rocks and
Gemstones by Borner he describes it as 'Falconseye' so I guess it
only a very short step from falcon to hawk.
I have included this excerpt re crocidolite:
This quartz composite stone begins as a fibrous blue mineral called
crocidolite, which is comprised of iron & sodium. In some resources
crocidolite is referred to as asbestos. The transformation begins as
clear Quartz becomes imbedded between the fibers of crocidolite. The
completed process will result in one of two a blue stone
called Hawk�s Eye or the golden brown stone called Tiger�s Eye. As the
gem forms the iron & sodium are completely dissolved, the quartz
takes on the fibrous formations & the blue color of crocidolite. This
creates the parallel lines within the gem giving it the liquid luster
& light movement the stone is so loved for. Even though the iron &
sodium dissolve, traces of hydrated oxide of iron deposit between the
crocidolite & Quartz, creating the yellows that are common to both
Hawk�s Eye & Tiger Eye. How much of this hydrated mineral is
deposited will determine how red, yellow or brown a Tiger Eye will
be. The rarer blue Hawk�s Eye will have only the slightest amounts.
Hope this helps to sort things out.
Keith Torckler, Cornwallis, New Zealand