ITACOLUMITE

This article appears in Volume V14, Page 887 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: INV-JED

ITACOLUMITE , the name given to a variety of porous yellow sandstone or quartzose schist, which occurs at Itacolumi, in thesouthern portion of Minas Geraes, Brazil. This

rock

is of

interest

INTEREST

for two reasons; it is believed to be the source of the diamonds which are found in

great

GREAT

numbers in the

district

DISTRICT

, and it is the best and most widely known example of a flexible sandstone. Itacolumite is yellow or

pale

PALE (through Fr. pal, from Lat. palms, a stake, for paglus, from the stem pag- of pangere, to fix; " pole " is from the same original source)

-brown, and splits readily into thin flat slabs. It is a member of a metamorphic

series

SERIES (a Latin word from serere, to join)

, being accompanied by clay-slate, mica schist, hornblende schist and various types of ferriferous schists. In many places itacolumite is really a coarse grit or fine

conglomerate

CONGLOMERATE (from the Lat. conglomerare, to form into a ball, glomus, glomeris; so also the general term " conglomeration " for a miscellaneous collection of things, gathered together in a mass)

. Other quartzites occur in the

district

DISTRICT

, and there is some doubt whether the diamantiferous sandstones are always itacolumites and also as to the exact manner in which the presence of diamond in these rocks is to be accounted for. Some authorities hold that the diamond has been formed in certain quartz veins which traverse the itacolumite. It is clear, however, that the diamonds are found only in those streams which contain the detritus of this

rock

.
On the split faces of the slabs, scales of greenish mica are visible, but in other respects the rock seems to be remarkably pure. If a piece which is a foot or two long and half an inch thick be sup-ported at its ends it will gradually bend by its own

weight

WEIGHT

. If it then be turned over it will straighten and bend in the opposite direction. Flakes a millimetre or two thick can be bent between the fingers and are said to give out a creaking sound. It should be noted that specimens showing this property form only a small part of the whole mass of the rock. Flexible rocks have also been reported and described from North and

South

SOUTH
SOUTH, ROBERT (1634–1716)

Carolina, Georgia, Delhi, and from the north of England (Durham). They are mostly sandstones or quartzites, but the Durham rock is a variety of the magnesian limestone of that district.
Some discussion has taken place regarding the cause of the flexibility. At one time it was ascribed to the presence of thin scales of mica which were believed to permit a certain amount of motion between adjacent grains of quartz. More probably, however, it is due to the porous character of the rock together with the inter-locking junctions between the sand grains. The porosity allows interstitial

movement

MOVEMENT

, while the hinge-like joints by which the particles are connected hold them together in spite of the displacement. These features are dependent to some extent on weathering, as the rocks contain perishable constituents which are removed and leave open cavities in their place, while at the same time additional silica may have been deposited on the quartz grains fitting their irregular surfaces more 'perfectly together. Most of the known flexible rocks are also fine-grained; in some cases they are said to lose their flexibility after being dried for some time, probably because of the hardening of some interstitial substance, but many specimens kept in a dry atmosphere for years retain this property in a high degree. (J. S. F.)

End of Article: ITACOLUMITE

If you wish, you can link directly to this article.

<a href="http://jcsm.org/StudyCenter/Encyclopedia/INV_JED/ITACOLUMITE.html">
ITACOLUMITE
</a>

(Previous)
ISYLLUS

(Next)
ITAGAKI, TAISUKE, COUNT (1837 )

JCSM was founded in 1997 and exists to help the community and bring people into a life-changing and productive relationship with Jesus Christ. JCSM offers over 200,000 free web pages, including its weekly inspirational emails that were sent continuously for over a decade.

Jesus Christ Saves Ministries
P.O. Box 9297
San Diego, CA 92169
1-888-887-0417 or Email