Veins, in geology, are sheet like bodies of crystallized
minerals found within rocks. The formation of veins is thought to
be the result of hot water precipitating the growth of crystals on
the walls of cracks and fissures that are found in rocks. Veins
usually grow on rocks at an incredible depth below the surface of
the earth measured in kilometers. There are really two mechanisms
likely for the formation veins, they are: open-space filling and
crack-seal growth.
For open space filling to take effect, the confining pressure is
generally considered to be low with a depth around 3-5 kilometers.
Many of these veins are capable of exhibiting rounded, globular
textures radiating out on the vein walls and filling up the open
space. Alternatively, hydraulic fracturing may create a breccia; a
rock composed of broken fragments filled in with vein material.
Crack seal growth occurs when the confining pressure is too
great, or where brittle conditions in rock are found. This method
forms very quickly during the deformation of rocks by precipitation
of minerals within the fractures. This is because pressures and
deformation mean that large open spaces cannot be maintained. The
space of one of these veins is usually measured in millimeters or
even micrometers. The veins can then grow in thickness by the
reopening of the vein fracture and more minerals being deposited on
the growth surface.
As a whole, veins need hydraulic pressure and some sort of open
space within the rock mass for crystallized minerals to grow. One
of the most recognized minerals found in veins is quartz. Quartz is
also the second most common mineral found in the Earth’s
crust. It can be recognized by its glassy luster, definitive
hardness. Quartz is a major component in granite.
Quartz comes in many shapes and colors. It can also be perfectly
clear. Translucent white quartz is called milky quartz. Rose quartz
is a milky pink color because of impurities such as titanium, iron,
and manganese. Purple quartz is called amethyst. Its color is due
to iron impurities along with "holes" of missing electrons in the
crystal. Citrine quartz is yellow in color due to iron impurities.
Green quartz is called prasiolite. Iron impurities are also the
reason for its color. Smoky quartz has a grey color due to "holes"
of missing electrons in combination with aluminum impurities.
To log a find on this EC, you must visit the sight and obtain
the information to answer these questions:
1 - What type of vein do you think is in the rock monument, open
space filling or crack fill growth?
2 - How many veins can you see?
3 - What is the width of the largest vein present? (use your best
judgment)
4 - What color is the largest vein and why? (use your best
judgment)
5 - What signs of quartz do you see at this monument?
Once you have the answers to the questions, submit them in an EMAIL
to me through geocaching.com. Only then may you log this EC found.
Please DO NOT post the answers in your found log. If I find that
you have not sent me the correct answers (using your best judgment)
or that you have posted answers in your log, I will reluctantly
have to delete your find.
With that being said, enjoy this extraordinary piece of geology
right here in our local park district.
Online sources used for writing this EC are www.wikipedia.org and
www.about.com