1. Gloria Gill GEO 543
Evaporites Lab
Evaporites:
McLeod 19
1) The mineralogy of the sample consists of mostly gypsum and some Anhydrite. The
arrangement is a columnar prisms that grow off the fine grained sediment.
2) The evaporite crystals developed on the water-sediment interface.
3) N/A
4) The environment of these particular evaporite crystals was most likely a deep water
environment (but its is hard to tell how deep) since it would have required a calm, undisturbed
environment for the crystal formation in a columnar prism arrangement.

2. McLeod 20
1) The mineralogy of the sample consists of gypsum prisms in a columnar arrangement.
2) The gypsum evaporite crystals precipitated within sediment.
3) The inclusions present in the grains give evidence for displacement.
4) The environment of these particular evaporite crystals was most likely a deep water
environment since it would have required a calm, undisturbed environment for the crystal
formation in a columnar prism arrangement.
McLeod 21

3. 1) The mineralogy of the sample consists of halite in a cubic arrangement.
2) They probably precipitated at the water surface and piled on to the sediment after water
evaporated
3) N/A
4) A shallow water environment or sabkah are the probable environments for the halite
formation.
5) The inclusions are large and cubic. Fluid inclusion are evident by the bubbles present in the
sample grains.
PR-5

4. 1) The mineralogy of the sample constitutes of gypsum with small inclusions of aragonite and
anhydrite arranged in form of veins.
2) It formed within sediment.
3) It formed via incorporation and displacement.
4) It was mist likely formed in a sabkah environment evident by the nodular and chicken wire
texture.
5) The probable sequence of sedimentation is an alternation between hydrous gypsum and
anhydrite. Although not evident, this sample most likely started as Gypsum, precipitated
from solution. The first top layer is of anhydrite that indicates an environment where water
had dried, and gypsum was dehydrated to form Anhydrite. This anhydrite was later exposed
to water and through hydration once again became Gypsum evident by the relic anhydrite
inclusions. This cycle is characteristic of the sabkah environment.
PR4-10

5. 1) The thin section is characterized by high birefringence silt sized particles and singular
gypsum crystal randomly distributed iron oxides. Also present are molds where larger
crystals dissolve away. Due to the shape these molds may have been gypsum. These molds
are partly filled with blocky calcite cements and Fe-oxides.
2) Evaporite crystals have precipitated within the sediment
3) Formed by replacement.
4) The environment where the evaporites developed in a high energy shallow water
environment or sabkah environment.
Castile

6. 1) Mineralogy: Massive Gypsum with calcite laminations that formed due to varves and seasonal
variations of input
2) Evaporite crystals have precipitated within the sediments
3) Formed by replacement.
4) The environment where the evaporites formed were probably in a deepwater environment due
to the fact that the deposits are extensive according to Professor Rasbury.
5) The minerals that formed the dark laminae are most likely calcite varves. These layers of
calcite have a dull birenfringes because the layers are rich in organic matter.
Chert:

7. 550014:
1) The relative proportions are major amounts of microquartz and minor amounts of mega-
quartz.
2) The textural relationship is depositional.
3) The chert is in a bedded plane form since the mega-quartz exists in the form of veins.
550001:

8. 1) The relative proportions are major amounts of micro-quartz.
2) Textural relationship is pore-filling.
3) This is nodular chert because the lack of organic matter or organism remnants.
GL1-4:
1) The relative proportions of the minerals are major amounts of microquartz, minor amount of
chalcedony and trace amount of megaquartz.
2) The textural relationship is depositional.
3) This is bedded chert because the chert is preserved within the fossils is in the form of
chalcedony.
550015:

9. 1) The relative proportions include major amounts of microquartz and some trace amount of
chalcedony and megaquartz.
2) The textural relationship is replacement where chert is replacing the carbonate.
3) The contact between carbonate and chert in low magnification is primarily sharp since there is
a clear divide between the chert and the carbonate. However under greater magnification the
contact appears to be gradual evident by an increased number of carbonate inclusions in the
chert near the contact.
550019:

10. 1) The relative proportions include major amounts of micro-quartz and minor amounts of
chalcedony, and trace amounts of mega-quartz.
2) The textural relationship is pore filling,
3) Chert replaces the original carbonate oolites, some are replaced by microqurartz and others by
macroquartz mosaic.
4) Chalcedony is a primary cement since it is between the grains and coats in layers across more
than one grain rather than replace grains.
5) Compaction features include grain fractures and dissolution of grains. See photograph
Iron-Rich Sediments

11. W-67:
AH014:
1) There is an ooltic grainstone texture which can be found more commonly in carbonates.
2) The nuclei of the oolites are hard to distinguish since they have been replaced by micro
crystalline quartz.
99:
1) The important textural feature is laminations which is comparable to laminations found in
carbonates and evaporites, however they are preserved here better.
Phosphorites

12. AJM 18: (I couldn’t find 575000…but this was in the phophorites tray
1) The non-isotropic materials found in the pelloids are micrite and are diagenetic.
2) The non-isotropic material between pelloids is massive and is detrital, unless it replaced an
oringal matrix which in that case it would be diagenetic too.
Monterey Phosphorite:
1) The black material might be organic material called collophane.
2) Collophane is non-crystalline phosphate which if metamorphosed turns to apatite. The
collophane in shell fragments represents organic material that has been replaced.
3) The host sediment might be made up of quartz (sandy and coarse grained), which is indicative
the environment the shell came from (maybe beaches).
Various Phosphorite Hand Samples: