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Dacite is a
highly knappable volcanic stone similar to Obsidian in many ways but
considerably more textured and less glass-like. Knappability falls midway
between cherts like Novaculite and Obsidian volcanic glass. Priority Mail Postage within the United States is pre-paid and
included in the price of this 20 lb box of 3-6 inch Dacite Spalls.
International Customers
should contact us for adjusted shipping and other
litmitations before purchasing.
Our cleaned and graded Dacite spalls range in size from
3-6 inch peices. This size is good for large and medium points and blades. We
highly recommend using gloves to work this material as it will make even
the most experienced knapper bleed.
WARNING: Dacite flakes can be sharper
than razor blades! Exercise extreme caution!
We strive to provide the cleanest, blemish
free knapping material within our means. On some spalls however, blemishes
do get past us because not all defects are evident at first or even second
inspection. In efforts to avoid defects as much as possible, we perform a
few thinning blows to ensure that you do not pay for large amounts of waste,
over thick spalls, or fragile/thin sizes that will shatter with the first
strike.
Large knapping material requires large billets. Attempting
to knap large stone with too small of a billet will damage the billet and not
produce sizable thinning flakes early on in the process as needed. If you are
graduating to this size material from one of our kits, we recommend adding a
large copper percussion billet to your order. If you are unsure about what you
need, please visit our Flintknapping Buyer's
Guide, or feel free to contact us and we will
be glad to
help.
General Information on
Dacite
Dacite is an igneous, volcanic rock. The word dacite comes from Dacia, a
province of the Roman Empire which lay between the Danube River and Carpathian
Mountains (now modern Romania) where the rock was first described.
Dacite
usually forms as an intrusive rock such as a dike or sill. Examples of this type
of dacite outcrop are found in northwestern Montana and northeastern Bulgaria.
Nevertheless, because of the moderate silica content, dacitic magma is quite
viscous and therefore prone to explosive eruption. A notorious example of this
is Mount St. Helens in which dacite domes formed from previous
eruptions.
Dacitic magma is formed by the subduction of young oceanic crust under a thick
felsic continental plate. Oceanic crust is hydrothermally altered causing
addition of quartz and sodium. As the young, hot oceanic plate is subducted
under continental crust, the subducted slab partially melts and interacts with
the upper mantle through convection and dehydration reactions. Once at the cold
surface, the sodium rich magma crystallizes plagioclase, quartz and hornblende.
Accessory elements like pyroxenes provide insight to the history of the
magma.
The formation of dacite provides a great deal of information
about the connection between oceanic crust and continental crust. It provides a
model for the generation of felsic, buoyant, perennial rock from a mafic, dense,
short-lived one.
From Wikipedia, the free
encyclopedia
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