Phoenix Zoo - Arizona Trail: A Geology Lesson EarthCache
Phoenix Zoo - Arizona Trail: A Geology Lesson
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This EarthCache is located along the Arizona Trail at the Phoenix Zoo. Admission into the zoo is required.
Zoo hours:
January 10 – May 31: 9:00AM - 5:00PM (daily)
June 1 – August 31: 7:00AM - 2:00PM (weekdays) 7:00AM - 4:00PM (weekends)
September 1 – November 2: 9:00AM -5:00PM (daily)
November 3 – January 9: 9:00AM – 4:00PM (daily)
Entrance Rates:
Adults $20 / Children 3-12 $10 / Under 3
UPDATED LOGGING REQUIREMENTS: (01NOV2013)
Along the "Arizona Trail", in the vicinity of the posted coordinates, you will find several examples of Arizona geology. Each display (once had) a plaque attached to it describing the feature, and where in Arizona it would naturally be found.
To claim a "Find" for this EarthCache, you must locate at least four of these geological samples, (determine) where else in Arizona you could discover the same feature, and email the cache owner with your answers. Any log that does not meet these requirements will be deleted.
Petrified wood (from the Greek root "petro" meaning "rock" or "stone", literally "wood turned into stone") is a type of fossil: it consists of fossil wood where all the organic materials have been replaced with minerals (most often a silicate, such as quartz), while retaining the original structure of the wood. The petrifaction process occurs underground, when wood becomes buried under sediment and is initially preserved due to a lack of oxygen. Mineral-rich water flowing through the sediment deposits minerals in the plant's cells and as the plant's lignin and cellulose decay away, a stone mould forms in its place. In general, wood takes less than 100 years to petrify. The organic matter needs to become petrified before it decomposes completely. A forest where the wood has petrified becomes known as a petrified forest.
Conglomerate is a clastic sedimentary rock that contains large (greater than two millimeters in diameter) rounded clasts. The space between the clasts is generally filled with smaller particles and/or a chemical cement that binds the rock together. Conglomerate can have a variety of compositions. As a clastic sedimentary rock it can contain clasts of any rock material or weathering product that is washed downstream or down current. The rounded clasts of conglomerate can be mineral particles such as quartz or they can be sedimentary, metamorphic or igneous rock fragments. The matrix that binds the large clasts together can be a mixture of sand, mud and chemical cement. Conglomerates often begin by being deposited as a sediment consisting mainly of small clasts as shown in the photo below. The finer size sand and clay which fill the spaces between the larger clasts is often deposited later on top of the large clasts and then sifts down between them to fill the interstitial spaces.
Igneous rock (derived from the Latin word "Igneus" meaning of fire, from "Ignis" meaning fire) is one of the three main rock types (the others being sedimentary and metamorphic rock). Igneous rock is formed by magma (molten rock) cooling and becoming solid. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Over 700 types of igneous rocks have been described, most of them having formed beneath the surface of Earth's crust. These have diverse properties, depending on their composition and how they were formed.
Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure (temperatures greater than 150 to 200 °C and pressures of 1500 bars) causing profound physical and/or chemical change. The protolith may be sedimentary rock, igneous rock or another older metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath the Earth's surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion. They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's interior. The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides us with very valuable information about the temperatures and pressures that occur at great depths within the Earth's crust. Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite.
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