 |
Pyrrhotite (salmon-coloured, Fe7S8)
enclosed in pyrite (yellow). The margins of the tabular pyrrhotite
crystals show replacement by pyrite. The pyrrhotite formed as a result of
hydrocarbon seepage. XRD and thermomagnetic measurements confirm the
mineralogy (width of image= 320mm) {RL optical,
oil immersion} |
Cement oil field, Oklahoma [R.L. Reynolds] |
 |
Pyrrhotite blades within a calcite matrix {RL
optical, oil immersion} |
[R.L. Reynolds] |
 |
bladed Pyrrhotite crystal (PO) (scale bar= 4mm)
{SEM} |
Cement oil field, Oklahoma. [R.L. Reynolds] |
 |
Pyrrhotite (Fe7S8, darker;
PO) intergrown with pyrite (white;PY), with later formation of marcasite
(MC) on the periphery. Composite grains such as this my represent a late
stage in the production of FeS2 phases. In this oil field
pyrrhotite forms approximately 0 to 5% of the total FeS2 (width
of image= 320mm) {RL optical, oil immersion} |
Cement oil field, Oklahoma. [R.L. Reynolds] |
 |
Detrital plant fragment. The cell lumens of
this fragment contain sulfide, with at least some of
it being greigite. Interpretation based on accompanying XRD and magnetic
properties (width of image= 320mm) {RL optical,
oil immersion} |
[R.L. Reynolds] |
 |
Grain morphologies of greigite particles less
than 0.1mm in size. Interpretation based on
x-ray diffraction and magnetic measurements (width of micrograph =4.5mm
){magnetic extract, TEM} |
Quaternary, Sheringham clays, Norfolk,UK [D.
Hallam] |
 |
Magnetic sulphide grain (Fe + S from EDS
analysis) inferred to contain or be greigite. The sulphide appears to be a
replacement of an organic structure and sits on a plant fragment. The
magnetic extract was highly unstable and became non-magnetic after a few
days, due to the oxidation of the greigite {magnetic extract, SEM} |
Iron age (~300-100AD) ditch, Yarnton,
Somerset, UK. [M.W. Hounslow] |
 |
Small particles of Fe plus S (interpreted as
greigite) on a large octahedra of pyrite (scale bar = 4mm)
{magnetic extract , SEM, EDS} |
Ninuluk-Seebee Formation, Cretaceous, Alaska
{R.L. Reynolds] |
 |
Individual single-domain greigite crystals.
Greigite was confirmed by XRD and EDS. (scale bar = 2mm)
{magnetic extract , XRD, SEM, EDS} |
Björkeröds
Mosse, southern Sweden {I. Snowball] |
 |
Martite (titanomagnetite replaced by
haematite). The typical trellis texture of haematite replaced
titanomagnetite is accentuated by voids, indicating some removal of the Fe
from the original grain. Few thin vestiges of darker ilmenite (FeTiO3)
emphasis the trellis texture (grain is 300 mm
across) {Optical, Oil immersion} |
Miocene Catahoula sandstone [R.L. Reynolds] |
 |
Polycrystalline haematite displaying trellis
textured martite, indicated by the optical anisotropy of the haematite
crystals. (grain is 90 mm across) {optical,
cross nicols} |
Permian, Cutler Fm, Utah [R.L. Reynolds] |
 |
Biotite grain which has been partially
altered to specular haematite. The haematite has formed parallel to the
cleavage planes of the biotite. Note the blood-red internal reflections of
fine-grained heamatite grains on the periphery of the altered biotite
(grain 100 mm across) {optical} |
Permian, Cutler Fm, Utah [R.L. Reynolds] |
 |
Clusters of specular haematite composed of
interlocking haematite blades. The blades sit on top of smectite {SEM} |
Permian, Cutler Fm, Utah [R.L. Reynolds] |
 |
Pyrite replacing titanomagnetite, with the
pyrite mimicking the 111 lattice planes of the host. (width of image 100 mm)
{RL optical} |
[L.Owens] |
 |
Titanomagnetite composed of relict magnetite
(MT) and ilmenite (ILM) has been replaced by pyrite (white). Marcasite
(MC) occurs as partial overgrowths on the pyrite. (width of image = 160mm)
{RL Optical, oil immersion} |
Miocene Catahoula Sandstone, Texas [R.L.
Reynolds] |
 |
Replacement of titanohaematite (gray) by
pyrite (white) on grain margins and along fractures. (width of full photo=
160mm) {RL Optical, oil immersion} |
Miocene Catahoula Sandstone, Texas [R.L.
Reynolds] |
 |
Fe and S spheres (interpreted as pyrite) on
an Fe-Ti grain (interpreted as titanomagnetite), which shows strong
dissolution. The upstanding ridges may be Ilmenite intergrowths, which are
more resistant to dissolution than the intervening Fe-rich
titanomagnetite. {SEM, EDS} |
Quaternary, Great barrier Reef, ODP hole 864,
Australia. [A.Perkins] |
