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Tripoli


#1
 I scraped off a bit of my tripoli bar, got rid of the matrix
with hot water, dried  the powdery stuff and peered at it with
a 40x and a 100x lens in my microscope. There were irregularly
shaped particles, but no diatoms I'm afraid. 

Hi John,

There are several kinds of tripoli, one being in fact
diatomaceous earth or terra silicea. In 1 cubic centimeter,
weighing .25 grams, there are about 1 thousand millions fossil
skeletons. I’ve got a photograph with a 1:1800 enlargement, and
the largest single diatomee is about 1 inch across.

American tripoli from IL and TN doesn’t contain diatomees, but
consists of 92% amorphous quartz, 1.3% iron (III) oxide, 3.6%
aluminium oxide and some other additions, colour off white to
yellow, mixed with tallow, other fats and C17H35COOH (stearine
acid? Don’t know the English name) for buffing.

German tripoli contains 78%-89% diatomaceous earth, 0.35%-1.8%
iron (III) oxide, 1.82%-5.28% aluminium oxide, is softer than
the American.

Rottenstone is a substiute for tripoli, 80%-85% silicon dioxide,
10% aluminium oxide, yellow-red to yellow-grey colour.

Artificial tripoli made of pure silicon dioxide, cristalline
quartz and sand.

regards, Markus


#2

According to Oppi book “Metal techniques for Craftsmen” Tripoli
"occurs in schistose deposits of silica, as a pulverised powder.
It is a common ingredient in a cutting compound mixed with a
grease to form bars and used on a buffing wheel to remove
surface scratches" I don’t what "schistose deposits of silica"
are. Anyone got any suggestions? Richard W UK


#3
According to Oppi book "Metal techniques for Craftsmen" Tripoli
"occurs in schistose deposits of silica, as a pulverised powder.
It is a common ingredient in a cutting compound mixed with a
grease to form bars and used on a buffing wheel to remove
surface scratches" I don't what "schistose deposits of silica"
are. Anyone got any suggestions?

Some sort of clay–I see Egyptian scarabs made of schist stone
(you can’t say that too fast!) all the time.