PYROCLASTIC MATERIAL RESEARCHES BY
SCANNING ELECTRON MICROSCOPY
*GOMEZ L. S. ** RODRIGUEZ L. A.
**INGEOMINAS Santafb de Bogotk Colombia, AA. 4865
email: lsgomez @trilobite.ingeomin.gov.co FAX 5712223764
“GEOSERVICES -Colombia - Transv. 40 No. 42-20 Bogota- Colombia South America
Studies of scanning electron microscopy, EDX analysis and optic microscopy allowed to
identify the presence of pyrociastic material; which has been classified for several years
as a sedimentary material, of recent deposits covering the Tertiary and lower
Quaternary sedimentary rocks in the Colombian Eastern Andes mountains range.
The material can be found in wide valleys with soft morphology; usually unconsolidated
or friable. It corresponds to detritical materials of pyroclastic rocks expelled from volcanic
vents, from recent volcanic events (because there are thermal phenomena related with
them like hot water springs enriched with sulphures). Carried out by air and deposited
upon land surface, in lakes or on lands, commonly eroded and transported by running
water and redeposited,
together
with elastic and chemical
material;
the tephras
are
covering quatemary deposits.
The analyzed material has rhyolitic composition and it corresponds mainly to volcanic
ashes. In Iza, one of the locations, the mixed material is mainly composed of crystal and
lithic-vitric tuffs. In Paipa the other location the rhyolitic tuffs are straight associated with
hot water and sulphurous emanations, generating salts and chalcedony as mineral
deposits.
The particles are ranging from 5u to 4 mm, and the average particle size is 0.05 mm.
The colorless glass is unaltered without any kind of devitrification. Most of the particles
are small and irregular pieces of glass, making part of volcanic ashes and tuffs.
In a common way this material is known as pumicite, for commercial purposes and it is
characterized by small particles of volcanic origin, with a very low density, occurring as a
powder from coarse to fine, in irregular bedded deposits, which are largely mined by
open-pit methods. After mining, crude pumice is crushed, dried and screened.
There are a lot of utilities for the volcanic ashes, the most important could be as a
puzzolanic material, and also is widely used as a carrier in insecticides. For Portland
cement the ashes have a fairly close composition as the raw argillaceous materials
commonly used so a product of a suitable uniformity can be obtained. Because of its
extreme finesse it requires no crushing or grinding.
Those materials could be used in concrete aggregates, approaching the natural condition
as a cementant material filling small pores to produce lightweight concrete. There seems
to have been in a recent volcanic event, because now there are thermal phenomena’s related
with them, like hot water enriched in sulphures, tuff and tephras covering quaternary deposits
The chemical analyses of the ash are very similar the results were compared between Paipa
and Iza Regions. In Portland cement the ash has the quality to have e a composition fairly close
to that of the argillaceous raw materials use s and may be used if a product of a suitable
uniformity can be obtained. Because of its extreme fineness it requires no crushing or grinding.
In general the deposits are uncosolidated, therefore the ash can be mined easily
For Portland cement the ashes have a fairly close composition as the raw argillaceous
materials commonly used so a product of a suitable uniformity can be obtained. Because
of its extreme finesse it requires no crushing or grinding.
Cryptocrystalline quartz with flint, textures,
forming chalcedony associated with tuffs
Unaltered volcanic ash and dust at
710 times (white line stands for 0.1
mm length)
Scanning
Electron
miuuphotograph
-~xMttu
* bkbmwmm.wIyI
amylnhdim.taRIglm
Unaltered wlcanic ash and dust at 710 times
(white line stands for 0.1 mm length)
Scanning Electron microphotograph. The
right non scaled , shows a detailed of the
volcanic ash
--*IIIoI
* “abmey*rclr
Black lllll - RlPl Region