From:
<jtwilley@xxxxxxxxxxx>
Date:
Mon, 24 Jun 2002 01:48:42 -0400
Subject:
Nodule in Limestone
Bev,
Unless I missed it you don't actually mention what color the nodule is and
whether it is opaque. What you describe sounds like it could be hematite, if
it is opaque and black to liver colored, or flint. Flint, as you might guess
from the name, strikes sparks from tool steel and may have a rust colored rind
but is rather nondescript in appearance. Hematite, or ferric oxide is not
magnetic if free of magnetite, and commonly grows in radiating crystals that
present a reniform (kidney shaped) surface to the outside. In this form the
broken surfaces are often dramatically faceted and highly reflective.
If the material is brassy in color on a fresh surface it could be marcasite or
pyrite, both iron sulfides which can develop an oxidized outer surface.
Marcasite often forms radiating masses.
John Twilley
- References
- message 00028: Nodule in Limestone - Beverley Wright (24 Jun 2002)
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