By the name of Allah
The following is adescription of how to make rock sections using the facilities in Cairo Uni., Geology Department that I have trained there for 10 days in .Rock sections facilities at other universities will probably have somewhat different equipment but these instructions will be largely correct anywhere. Making section is both an art and a science. We have sufficient equipment so that the art aspects are relatively minor, but every rock is different and technique can best be learned by perseverance and practice.
There are four methods for making sections depend on which of the following i want to study
1- transparent minerals --> thin section method
2- opaque minerals -->polish method]
3- both transparent and opaque minerals --> thin polish method
4- fluid inclusion --> double thin polish method
The following is adescription of how to make rock sections using the facilities in Cairo Uni., Geology Department that I have trained there for 10 days in .Rock sections facilities at other universities will probably have somewhat different equipment but these instructions will be largely correct anywhere. Making section is both an art and a science. We have sufficient equipment so that the art aspects are relatively minor, but every rock is different and technique can best be learned by perseverance and practice.
There are four methods for making sections depend on which of the following i want to study
1- transparent minerals --> thin section method
2- opaque minerals -->polish method]
3- both transparent and opaque minerals --> thin polish method
4- fluid inclusion --> double thin polish method
We will discuss now each of the above methods in detail after giving an overview to the topic
Overview
When we make a section, we must cut the rock normal to the layers in order to see all layers in our section but if the rock is in a massive form ( i.e. haven’t stratification, e.g. limestone or dolomite) we can cut any way
[The edge of the saw that cut rock is made of diamond alloy that is the hardest mineral known to us and so can cut any rock]
[There are a lot of saws which is used for different types and sizes of rocks
[Grinding minerals is done by a powder called carbocorundum which has a different scales range from rough to smoother powder ( 600 à 400 à 320 à 240 à 200)
[Note: this scale represent the no. of grains that pass through one centimeter square of sieve and so as the no. of grains increased it become smoother and become more accurate that make the grinding for the very small particles in the chip]
[Grinding is done on the grinding wheel in its early stages then on a glass ]
plate in the last stages
Epoxy is made up of harden and raisen solutions that are mixed together in a certain proportion depend on the order of the client
In prosity and permeability studies we use a certain solution called blue-dye through mixing it with epoxy.This method has an important role in oil industry in estimating if the oil. The function of the mix is to enter into the pore spaces between grains and through that we can estimate the value of prosity and permeability of rock. is present in a commercial ratio (from prosity) and in a large area (from permeability
Methods of making different types of sections
thin section
What is the thin section?
A thin section is a 30 µm (= 0.03 mm) thick slice of rock attached to aglass slide with epoxy
Why do we do thin sections?
Answer: to show transparent minerals (minerals that transmit light through it in the optical microscope, e.g. Qz, Orthoclase, pyroxene …etc.)
We study these sections under the polarizing microscope
1-turn on the saw and then cut the rock normal to the layers in order to show all layers in your thin section and be sure from cooling the saw edge with water or oil if the rock sample is dissolve in water (e.g. Gypsum, Clay, Mud… etc.)
2- after the cutting is complete, grind your sample by carbocorundum powder on the grinding wheel from hard to smoother powder ( 120à 240à320
3- then gring the sample on a glass plate by also the carbocorundum powder by the 400 and 600 powder
4-heat the sample on the heater then cool it and put the epoxy or Canada balsam on it to be in a contact with the slide
[5- grind it again by grinding wheel and glass plate during examine it under the microscope once by once in order not to make a fail in the section
6- at last put a cover on it and make it in a contact with Canada balsam
A thin section is a 30 µm (= 0.03 mm) thick slice of rock attached to a glass slide with epoxy
2-Polish method
Why do we do polish method?
Answer: In order to see opaque minerals (minerals that didn’t transmit light through it, e.g. gold, iron cupper …etc
We study it under a special type of microscope that enables us to see
opaques
Steps
cut the sample to a one cm thickness
2- merge it with epoxy in a 2 inch plate and leave it for 24 hours to make a complete drying for it
Polish it with the smooth powder ( 400 or 600)
Polish it again manually with gookha or by the automatic machine by one of that two powders ( chromo oxide –green colour- or iron oxide – red
الجوخه عبارة عن قماش أخضر يوضع على قرص حديدي ثم يثبت عن طريق إسورة حديدية على مقاس القرص
3- Thin polish method
Why do we do thin polish method?
Answer: In order to see the transparent and opaque minerals and study their properties but this method is too expensive
Steps
As we do in the last method but in a very thin section compared to the normal polish method that we grind it to a certain thickness while the polish section has nearly 1 cm thickness
[4- Double thin polish method
Why do we do this method?
Answer: to see fluid inclusion and study porosity and permeability
Steps:
We do it as the last method but here we make polish from both sides of the rock chip and study it under the polarizing microscope
عدل سابقا من قبل في 2007-09-29, 6:42 pm عدل 2 مرات
