Dear Erhan,

The following publication might be helpful:

The procedure employed in cutting thin sections of gypsum follows the

same general pattern as that of ordinary rock thin sections, but the softness

of the mineral and the low temperature at which it tends to undergo

a transition to the hemihydrate present unusual difficulties.

A slice is cut from the hand specimen or drill core on the diamond saw.

With this soft mineral grinding on the rough lap is not necessary. The

first grinding takes place on the medium lap with l1F silicon carbide to

remove saw marks and to cut the slice down uniformly to about f in. in

thickness. If f in. can be achieved, very little grinding on the medium lap

is necessary to remove saw marks. Soft minerals like gypsum require

special care in getting a fine-ground surface prior to mounting on the

glass slide. This operation is thus a critical one in the procedure. Number

600 silicon carbide serves as the grinding abrasive on the fine-grinding

lap. Grinding on the fine lap is continued until further grinding does not

improve the smoothness. Scratches and also a finely pitted surface develop

during this grinding. To remove them, grinding is resumed on the

plate glass with 1600 optical alundum. The key to producing a smooth,

scratch-free surface is the pasty consistency of the mixture of the alundum

and water. If the mixture is too watery, the grains of alundum flow

too freely and form scratches even though this abrasive is very fine and

of even texture. By a gentle, steady rubbing forward and backward on

the glass plate, a smooth, scratch-free surface is obtained. A Iittle practice

is necessary to get the best results.

The gypsum slice is next mounted on the glass slide with Canada balsam.

As gypsum loses part of its water of crystallization and water absorbed

between cleavage planes at a low temperature, bubbles are readily

formed and must be guarded against. Therefore chips are not heated but

are allowed to dry overnight at room temperature before being cemented

to slides.

For mounting, the slide and chip are heated on the brass mounting

table just enough so that the hard-cooked Canada balsam will flow fairly

easily and allow pressing the slide down on the chip and squeezing out

excess balsam. Keeping the temperature low prevents the formation of

1200 FRANK S. REED AND JOHN L. MERGNER

bubbles (as mentioned above). But difficulty will be experienced in getting

a good mount the first time because the balsam, while flowing fairly

easily, is not as fluid as it would be at a higher temperature. Generally

the operation has to be repeated several times before all bubbles are removed.

After the chip is cemented to the glass slide, grinding is resumed

on the medium lap. Number 1F silicon carbide serves as the abrasive for

this grinding. For good results the gypsum chip is ground down no

thinner than sle: in. The next and final grinding on the revolving lap

follows the usual procedure in the preparation of ordinary rock thin sections.

Here it is well to grind down the section until the gypsum shows a

bright-yellow interference color under crossed nicols. An attempt to secure

a thinner section might result in the complete grinding away of the

section. Final grinding is done on plate glass with I 600 optical alundum

until the required thinness is obtained. It may not always be possible

to cut the section down to a thinness to permit gray to show under the

crossed nicols because of a tendency for the section to fray at the edges.

Usually gypsum sections show pale yellow under crossed nicois by the

time fraying begins. Once fraying begins, it progresses rather rapidly,

and therefore grinding must be stopped before the section becomes very

small or is lost entirely. A pasty mixture of water and alundum is necessary

to prevent scratches when a fine surface is to be ground on the

mounted gypsum chip.

The cover glass is mounted after the various stages of grinding are

completed. This proceeds partly along the same lines as in the preparation

of ordinary rock thin sections. As mentioned before, the use of minimum

heat is an important factor. To avoid any danger of overheating,

the cover glass is mounted by cold mounting, as described above. The

slide is placed in the electric oven at 50o C. and allowed to remain overnight,

so that the balsam becomes hardened about the edges of the cover

glass. The excess balsam around the edges is removed with a knife, just

hot enough to permit the scraping away of the balsam. If too hot, it

causes sufficient melting of the balsam to form bubbles under the cover

glass. It is necessary, after the first scraping, to place the slide in the oven

again overnight at the same temperature to allow the balsam under the

cover glass to harden to a greater depth from the edges inward. On removing

the slide from the oven this second time, a little more balsam will

be found to have oozed from under the cover glass. This is also scraped

away with a hot knife. In most cases the balsam under the cover glass

has had sufficient volatile matter driven off so that it is hard enough to

permit washing off of the remaining film of balsam adhering to the slide.

Only experience enables one to determine how far this procedure should

be carried. The slide is washed in alcohol with a hand brush and quickly

PREPARATION OF ROCK THIN SECTIONS

immersed in water to prevent the alcohol from eating under the edges of

the cover glass, after which it is dried with a soft cloth. As a safeguard

against the possibility that the balsam is not sufficientiy hard and to prevent

stickiness about the edges of the cover glass, it is a good plan to

place the slide back in the oven for another night.

To view the full publication, please see attached file.

Hoping this will be helpful,

Rafik

merhaba Erhan, bana adımları verebilir misin ?

şimdiden teşekkür ederim. Erhan Karakuş