Otto Jarstad is a beautiful park hidden off Belfair Valley Road. Most people pass this park and don't realize it has much to offer.
This park has some geology ready for you to discover, with some great signs to help you understand what you are looking at.
This Earthcache will take you on an adventure to discover some of the geology the park has to offer.
Igneous rocks
are “fire-born,” meaning that they are formed from the cooling and solidification of molten (melted) rock. The word igneous derives from ignis, the Latin word for “fire.” Molten rock material is known as magma until it is erupted onto the surface when it then is termed lava.
There are two broad types of igneous rocks:
Intrusive (Plutonic) Rock Classification
Intrusive rocks are classified on the proportion of major minerals in them, particularly the relative amounts of quartz, alkali-feldspar, and plagioclase. Mafic and intermediate intrusive rocks also have a significant proportion of minerals that contain iron and magnesium such as olivine, pyroxene, amphibole, and biotite. The different types of mafic intrusive rocks are classified on their relative amounts of olivine, pyroxene, and plagioclase.
The minerals found in the three main types of plutonic rocks are:
- Granite consists mostly of quartz and alkali-feldspar, with relatively minor plagioclase feldspar and mafic minerals (biotite, muscovite and/or amphibole [hornblende]).
- Diorite consists mostly of plagioclase feldspar, amphibole, and pyroxene.
- Gabbro consists mostly of pyroxene, olivine, and plagioclase feldspar.
Extrusive (Volcanic) Rock Classification
Volcanic rocks are classified based on their chemical composition as determined by analytical techniques that identify the proportion of major elements found in them. Unlike for plutonic rocks, it is not possible to classify volcanic rocks based on the minerals found in them.
Some volcanic rocks contain some crystals (phenocrysts) that grew in the magma chamber prior to eruption, but others contain no crystals at all or are volcanic glass (obsidian).
In addition to the mafic (low silica) basalt, and the silicic rhyolite, several subdivisions exist between the two compositional end members.
Sedimentary rocks
are formed from deposits of pre-existing rocks or pieces of once-living organism that accumulate on the Earth's surface. If sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock. These rocks often have distinctive layering or bedding and create many of the picturesque views of the desert southwest. Sedimentary rocks are classified into three groups: Clastic, Biologic, and Chemical.
Clastic Sedimentary Rock
Clastic sedimentary rocks are made up of pieces (clasts) of pre-existing rocks loosened by weathering. These rocks have particles ranging in size from microscopic clay to huge boulders; their names are determined by the clast or grain size. The smallest grains are called clay, then silt, then sand. Grains larger than 2 millimeters are called pebbles.
Biologic Sedimentary Rock
Biologic sedimentary rocks form when living organisms die, pile up, and are then compressed and cemented together. Types of biologic sedimentary rock include coal (accumulated plant material that is carbon-rich), or limestone and coquina (rocks made of marine organisms).
Chemical Sedimentary Rock
Chemical sedimentary rocks form by chemical precipitation that begins when water traveling through rock dissolves some of the minerals. These minerals are carried away from their source and eventually redeposited, or precipitated, when the water evaporates away.
Metamorphic rocks
form when high temperatures and pressure act on a rock to alter its physical and chemical properties (metamorphism means 'to change form'). These conditions often stretch, twist and fold the rock as it cools. In metamorphic rocks some or all of the minerals in the original rock are replaced, atom by atom, to form new minerals. Types of metamorphic rocks include gneiss, quartzite, marble, schist, soapstone, and phyllite.
Foliated Metamorphic Rocks
As pressure squeezes on a parent rock during recrystallization it causes the platy or elongated minerals within the rock to become aligned, or foliated. Foliated rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied in.
Non-foliated Metamorphic Rocks
Not all parent rocks have platy or elongated minerals and when these rocks undergo metamorphism the individual mineral grains do not align. Types of non-foliated metamorphic rocks include marble, quartzite and hornfels.
Reference
National Park Services. (2022, September 26). Rocks. National Parks Service. https://www.nps.gov/subjects/geology/rocks.htm
⛰️Logging This Earth Cache⛰️
Please send me your answers to the following questions before logging this cache. (Answers can be sent through the message center):
1. What type of rock is at the first stage? (Igneous, Sedimentary, Metamorphic)
2. Based on your observation and the reading what is the subtype for this rock? (Example- Foliated Metamorphic, Biologic Sedimentary, etc.)
3. How is the rock at the first stage formed?
4. What type of rock is at the second stage location? (Igneous, Sedimentary, Metamorphic)
5. Based on your observation and the reading what is the subtype for this rock? (Example- Foliated Metamorphic, Biologic Sedimentary, etc.)
6. How is the rock at the second stage formed?