This EarthCache was developed with permission of the Hawk Woods
Nature Center. Hawk Woods offers endless opportunities for outdoor
recreational activities. This unique facility offers groomed nature
trails, a marsh boardwalk, a heated restroom/shower facility open
year-round, a covered picnic shelter that can be reserved in
season, a two-story Log Cabin Lodge with six overnight camping
cabins, all complimented by 80 acres of beautiful woods, meadows
and marsh.
The posted coordinates will bring you to a special rock just off
the parking lot at Hawk Woods Nature Center. This rock was
discovered on site during some excavation.
This rock was formed a billion years ago in the river channels of
northeast Canada. During the glaciation, it was pushed down through
Eastern Michigan from Ontario Canada by the glaciers.
Rocks are aggregates of minerals. Some rocks are made up entirely,
or almost entirely, of a single mineral; limestone made of calcite
and rock salt made of halite are two examples. More often, however,
rocks are composed of several kinds of minerals.
The three main types of rock are igneous, sedimentary and
metamorphic. Each of these terms gives a general idea of the way in
which that particular rock type forms. Igneous rocks solidify from
molten magma. Sedimentary rocks are deposited either as fragments
from some preexisting rock or as chemical precipitates, and under
normal earth surface temperatures and pressures. Metamorphic rocks
are formed by alteration under great heat and pressure from
preexisting rocks of any of the three types. These rock
classifications are field classifications. They can be used without
the aid of a microscope or other expensive equipment. More
elaborate classifications have been made, but these mainly involve
further subdivision of the field classifications. Field
classifications of rocks are based primarily on the texture of the
rock and upon its mineral composition.
The term texture means the size, shape, and arrangement of the
constituent mineral particles. The term is used in slightly
different ways for each of the three main rock types.
The texture of an igneous rock is determined by the degree of
crystallinity (crystal faces well formed and obvious, or not so)
and in the size of the crystals. The principal textures of igneous
rocks are granular (grained with individual crystal grains),
aphanitic or dense (mineral grains too small to be seen by the
naked eye), glassy (noncrystalline or microcrystalline), and
pyroclastic (composed of volcanic fragments).
The texture of a sedimentary rock depends upon the nature of the
particles (pieces of shells, differently sized fragments of rocks
and minerals) and the manner in which the particles are bound
together. The binding agent may be a cement carried into the
sediment and deposited around the particles, or the rock may be
held together by the intergrowth of the constituent mineral grains
in the case of mineral chemical precipitates. The two main
sedimentary rock textures are clastic (fragmental, detrital) and
nonclastic (chemical precipitates).
The texture of metamorphic rocks are dependent on differences in
orientation or alignment of the crystals and on the size of the
crystals. The two general textural types are foliated (the crystals
are aligned parallel with one another) and nonfoliated.
The mineral composition of the rock may be revealed to some extent
by its general color.
To get credit for this EarthCache, email the answers to 1,2, and 3
through my profile. If you take any pictures, please post them with
your log. Pictures are not required but are appreciated.
1) Is the rock igneous, sedimentary, or metamophic? Please give
reasons for your choice.
2) What is the texture of the rock based on the definitions
provided on this cache page?
3) Describe the color(s) of this rock.
4) OPTIONAL: Take a picture of the rock with you and/or your GPSr
and post it with your log.
I have earned GSA's highest achievements:
  |