The document discusses neomorphism, which is a diagenetic process where pre-existing minerals are consumed and replaced by new crystals of the same mineral or polymorph. Neomorphism destroys original textures and fabrics. It occurs most prominently in the meteoric and subsurface diagenetic environments through dissolution-reprecipitation processes. The document also includes examples and images showing neomorphism processes in carbonate rocks from West Virginia, where pre-existing micrite and skeletal grains are replaced by microspar and neospar crystals.

1. J_F_KAREEM@yahoo.com

2. Diagenesis of sediments includes processes with conspicuous effects,
such as cementation that transforms unlithified sediments into hard
limestones, quartz sandstones, or cherts. Diagenesis also involves the
dissolution of sediments to produce small pores to large cave systems.
Diagenesis also includes more subtle processes such as the alteration
of marine trace element and stable isotope composition, In carbonate
sediments,(Bathurst 1975).
Neomorphism in carbonate rocks such as limestone is often
increasingly which lead to forming the crystals with larger size,
(James, N.P., 1991).

3. 1-1introduction.
1-2 Neomorphism.
2-Some previous studies were Neomorphism been noticed
3-summary
references

4. Diagenesis includes all the chemical, physical, and biological changes
that occur after deposition, before metamorphism.(Friedman and
Sanders, 1978).
One of the Changes That Occur Within Rocks during Metamorphism
is Neomorphism that it is A comprehensive term for all diagenetic
transformations between one mineral and itself or a polymorph,
whether the new crystals are larger or smaller or simply differ in
shape from the previous ones.
During neomorphism Pre-existing minerals/crystals are gradually
consumed and their place in the same time occupied by new crystals
of the same mineral or a polymorph, (Folk, 1965).

5. 1-2 NEOMORPHISM
Carbonate diagenesis takes place in three major regimes or realms:
marine, meteoric and subsurface.
1-2-1 Marine realm
Includes the seafloor and the very shallow marine subsurface (Marine
Phreatic environment) .
strong dissolution of aragonite and calcite at two dissolution levels.
1-2-2 Meteoric realm
Meteoric Vadose environment Above water table, between land surface
and meteoric phreatic zone
Principal diagenetic processes:
Dissolution, alteration of aragonite and high-Mg calcite to calcite.

6. 1-2-3 Subsurface realm
Burial environment
Principal diagenetic processes:
Physical compaction, chemical compaction, and additional chemical
or mineralogical changes that may include dissolution, cementation,
aragonite-to-calcite transformation, and replacement of calcite by
another mineral such as dolomite.

7. Neomorphism occurs in all three diagenetic realms but is particularly
important in the meteoric and subsurface diagenetic environments,
FIG (1). This process destroys original textures and fabrics and, when
pervasive, may cause the entire rock to become recrystallized,
(Boggs,2006).
During neomorphism New minerals form from chemical reactions
between pre-existing minerals. And we can say that there is not
necessarily any change in the chemical composition of rock.

8. FIG (1) The principle environments in which post depositional modification of
carbonates occurs (from moore,c.h.,1989).

9. The atoms present in the rock simply rearrange to form new minerals.
This happens if the pre-existing minerals are chemically unstable at
metamorphic pressure and temperature (P&T) conditions. They react to
form new, stable minerals. The metamorphic minerals that form
provide information on the conditions (P & T) of metamorphism. This
means That you can estimate the P & T of metamorphism (especially T)
of many rocks based on the minerals present in the rock. For example,
the presence of biotite & garnet together in a rock indicates
metamorphism at (~850oF). However, some minerals are very resistant
to Neomorphism; a prime example is quartz. Neomorphism happens in
many rocks during metamorphism, and it often occurs in combination
with recrystallization,(Metamorphic rocks handout, GEOL 1010, M. Bunds Instructor).

10. 2-1 West Virginia, Wood County Trenton Formation, 9538ft.
(http://www.wvgs.wvnet.edu/www/tbr/Data/Petrology/FIGURES/APPENDIX_II/Diagenesis_Final2.pdf)
There is only neospar
evident in this thin
section. The lack of
skeletal grains suggests
that this rock was
completely comprised
of micrite prior to
Neomorphism, Fig (2). FIG(2)

11. This thin section is also
dominated by microspar,
although there are some
remnants of skeletal
grains. The skeletal
remnants suggest that the
rock was originally a
wackestone. There is some
micrite preserved between
the neospar grain contacts,
FIG (3).
FIG(3)

12. 2-3 West Virginia, Wood County Trenton Formation, 9795ft.
The neospar in this thin
section is slightly
coarser than that
observed above. There
are also more abundant
skeletal remnants
present, FIG (4).
FIG4

13. 3-Summary
------Neomorphism is
-One of the major processes operating in carbonates and include all
transformations between one mineral and itself or a polymorph.
-A major driving force for this is the metastability of aragonite, and, to
a lesser extent, high-magnesium calcite.
-This process generally results in an increase in crystal size, and may
lead to the destruction of all primary textures and features.
-Most neomorphism are a grading, leading to a general increase in
crystal size. It occurs generally in fine grained limestones,

14. -Degrading neomorphismis not common, but has been recorded.
-Neomorphism a wet process, involving dissolution-reprecipitation.

15. REFRENCES
1- Bathurst, R. G. C. (1975) Carbonate sediments and their diagenesis.
Elsevier, Amsterdam.
2- Friedman, G. M. & Sanders, J. E. (1978) Principles of Sedimentology.
John Wiley & Sons, New York, 792 pp.
3- James, N.P., 1991, Diagenesis of carbonate sediments, a short Course:
Geo.Soc.
4- Folk, R. L. (1965) some aspects of recrystallization in ancient
limestones. In: Dolomitization and Limestone Diagenesis.
5- Sedimentary Geology Dept. Earth Sciences National Central U.
Taiwan Prepared by Dr. Andrew T. Lin.

16. 6-Metamorphic rocks handout, GEOL 1010, M. Bunds Instructor.
7-Esmat, A. Abou, El-Anwar and Hamed, S.Mekky.
8-http://www.wvgs.wvnet.edu/www/tbr/Data/Petrology/FIGURES/
APPENDIX_II/Diagenesis_Final2.pdf