Ed Hitchkite was the creator of this Coal Fountain. They wanted to honor the workers that shaped the town's history. Since coal would not hold up as well under outdoor conditions, it was decided to use black granite instead. The black granite came from a quarry in Wisconsin. So this earthcache will focus on granite.
What is granite?
Granite is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. The word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. By definition, granite is an igneous rock with at least 20% quartz and up to 65% alkali feldspar by volume.
The term "granitic" means granite-like and is applied to granite and a group of intrusive igneous rocks with similar textures and slight variations in composition and origin. These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals, which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter color minerals. Occasionally some individual crystals (phenocrysts) are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is known as a granite porphyry. Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids.
Granite differs from granodiorite in that at least 35% of the feldspar in granite is alkali feldspar as opposed to plagioclase; it is the potassium feldspar that gives many granites a distinctive pink color. The extrusive igneous rock equivalent of granite is rhyolite.
Granite is nearly always massive (lacking any internal structures), hard and tough, and therefore it has gained widespread use throughout human history, and more recently as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm3, its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3–6 • 1019 Pa·s.
Efflorescene
We have all seen it. That chalky white powdery residue that is evident on newer brick, block masonry, and rock projects. Unfortunately, it can also occur on newer stone installations as well. That chalky white powdery residue is called efflorescence.
Efflorescence is a natural occurrence when using cement-based products subject to exterior or wet environments. Efflorescence is crystallization of soluble slats that are carried to the surface of the stone or grout joints. There are three things that need to occur in order for efflorescence to manifest itself.
1. Presence of soluble salts in any of the following:
- The substrate.
- Water used on site.
- High sodium chloride content, caused by water softeners often used in conjunction with wells.
- High sodium chloride content in concrete accelerators.
- Setting bed or installation materials.
- Finish materials.
- Close proximity of the project to a source of soluble salts.
2. A vehicle to carry the salts to the surface (e.g. moisture flowing through the installation system). This can occur when penetrations and wall caps are not detailed correctly. If moisture can be controlled, even if the salts exist, they may never make it to the surface.
3. A mechanism that can "draw" the salts to the surface. Usually, moisture will travel from cooler environments to warmer environments. This can occur in exterior applications when the sun shines and warms the surface of the stone. The moisture will be drawn to the surface as it carries the soluble salts with it. The salts will then crystallize and be deposited on the surface of the stone or grout joints. This phenomenon can also occur in indoor applications when moisture travels from the cooler areas beneath a concrete slab to the warmer air above the slab. Normal atmospheric humidity and temperature variations can be enough to draw efflorescence to the surface.
Logging Requirements
1. Why was granite used instead of coal for this fountain?
2. Describe the texture of the granite.
3. Describe the color of the granite. What does this tell you about the amount of feldspar present?
4. Look at the crystals in the granite. What do they look like? What color are they? How big are they?
5. Describe the efflorescence present during your visit.
6. Post a picture of yourself (face not required) or a personal item at the "Coal" fountain.