Monuments and Memorials in Harrisburg, PA
Harrisburg, as with any other capitol city, is filled with monuments and memorials. They are dedicated to people from every sector including workers, soldiers, politicians, victims, peacemakers and many more. Some examples are the Workers Memorial/AFL-CIO (workers), Soldiers and Sailors Memorial Bridge (soldiers), Gov. Andrew Curtin (politicians), Holocaust Memorial (victims) and The Rev. Dr. Martin Luther King Jr. Monument (peacemakers). These monuments are made from many different materials from simple bricks to bronze and granite. The website below gives a great list of some of the monuments around the city.
https://www.pennlive.com/erry-2018/02/daaf2c1ef2/monuments_and_memorials_in_har.html
This cache focuses on two of these monuments. They are conveniently located near each other, and near the capitol building. (Parking can be a little tricky, particularly during business hours, so you may have to walk a ways to get to them). The two monuments that you will be visiting are the Governor John Hartranft statue and the U.S. Senator Boies Penrose monument. The posted coordinates take you to the first one, and the waypoint coordinates take you to the second one.
Earthcache Requirements
Visit both monuments. The bases are both granite but are very different. Inspect both bases and answer the questions below based on your observations and on the text below.
- After looking at both granite bases list 2-3 obvious differences between them.
- Look at the size of the crystals. Which base has the larger crystals (red or gray)?
- Based on your answer to question 2 and the text below, which base (red or gray) was probably located deeper within the earth and cooled more slowly?
- Do you see any evidence of any of the potential problems with granite that are listed below? If not, just say that. If you do, list the problem(s) that you see.
- Post a picture at or near one of the monuments, but do not include any spoilers. The picture should include either you or a recognizable item such as a gps. This is your signature that you were there.
Granite
Rocks can be classified into three types: Igneous, Sedimentary, Metamorphic.
- Igneous rocks are formed when molten rock cools and solidifies. Pumice and basalt are examples of igneous rocks.
- Sedimentary rocks are formed as particles settle out of water (or possibly air) and accumulate in layers. Over long periods of time the weight of the upper layers eventually cements these particles into rock. Sandstone and shale are examples of a sedimentary rocks.
- Metamorphic rocks originated as either igneous or sedimentary rocks. Under the right conditions of heat, pressure and water the rocks undergo a change with new minerals forming and some of the original minerals getting carried away by water. Marble and slate are examples of metamorphic rocks.
Granite is an igneous rock which is composed primarily of feldspar and quartz. Feldspar is the most abundant mineral on earth, and granite is the most abundant igneous rock on earth. The American Society for Testing and Materials (ASTM) defines granite as a “visibly granular, igneous rock generally ranging in color from pink to light or dark grey, and consisting mostly of quartz and feldspars, accompanied by one or more dark minerals” Some of the other minerals that might be present include mica, horneblend and pyroxene. The combination of all the minerals that are present in the granite help to determine the color and grain structure of the rock. It is interesting to note that “black granite” is not really a true granite. For a rock to be considered granite it must contain high levels of feldspar and quartz, while “black granite” has little or none of either. It is, however, an igneous rock which is often used interchangeably with granite.
Cooling Rate and Crystal Size
The size of crystals in an igneous rock is an indicator of the conditions where the rock formed. An igneous rock with large crystals probably indicates that the rock formed deep within the Earth where it cooled slowly giving time for crystals to grow. An igneous rock with small crystals probably indicates that the rock formed close to the surface where it cooled rapidly and did not allow time for crystals to grow very big. Some magma cools so quickly that no crystals form.
Typical Uses for Granite
Granite is one of the hardest rocks available. On the Mohs hardness scale (which is used for measuring mineral hardness) granite has a hardness of about 6.5 out of 10. The hardness comes from the hardness of the constituent minerals, mainly Quartz (7) and Feldspar (6). A diamond is the standard for the 10 rating. Granite in its’ natural form looks like just another rock, but the hardness makes it a rock that can be polished to a very fine finish. That characteristic makes it very suitable for monuments and other building applications.
Granite is often used as a building material because it is much harder and more durable than other rocks. An important feature is that granite is not soluble in acid, so things such as acid rain do not affect the material. It makes it the perfect rock to use for outdoor structural and decorative applications. It can be found in many places such as:
Sculptures
Sculpture bases
Structural and veneer building stones
Architectural trim
Grave markers
Possible Issues with Granite
Blistering: This condition starts with a swelling of a surface layer, and can eventually burst through a thin layer. One of the most common causes of this is road salt, so this condition is most likely to occur near the ground.
Chipping: Chipping is a common problem with harder materials. It is usually caused by some sort of mechanical impact.
Cracking: Cracking is often another mechanical problem caused by overstressing the material in a structural application.
Efflorescence: This is a whitish deposit on the surface which give the rock a hazy appearance.
Erosion: In general, erosion is the wearing away of material which may be caused by water, wind, or windblown particles. It may result in some loss of feature definition, but since granite is quite hard the impact of erosion should be less than for other rocks.
Flaking: This is usually caused by water wicking into the material and freezing.
Staining: Stains might appear on the granite, but are usually produced by external causes such as bird droppings, iron or steel mechanical fasteners or graffiti.
References:
https://www.pennlive.com/erry-2018/02/daaf2c1ef2/monuments_and_memorials_in_har.html
https://www.amnh.org/exhibitions/permanent/planet-earth/how-do-we-read-the-rocks/three-types
https://www.gsa.gov/node/88304?Form_Load=88557