Box Vale - Rock School EarthCache

Earth Cache

You will be walking along The Box Vale Tramway. It was built in 1888 to carry coal mined in the Nattai Gorge to the main southern line at Mittagong. The line passes through several cuttings, a tunnel, and it ends at the "incline" by which coal was brought up from the gorge. The Colliery was closed in 1896 and the tramway was abandoned until 1996 when it was opened as a four-and-a-half kilometer bush walking track. Additional information and maps are available from the Visitors Information Centre in Mittagong.

You will probably lose Mobile phone reception as you get closer to the lookout.

Geology 101

Geology is the study of the Earth, the materials of which it is made, the structure of those materials, and the processes acting upon them. It includes the study of organisms that have inhabited our planet. An important part of geology is the study of how earth's materials, structures, processes, and organisms have changed over time.

One of the fundamental tasks facing geologists is the identification of rocks and minerals. Of course, you don't have to be a geologist to know what a rock is. Anybody can pick one up as they walk along and throw it at something. What a geologist does, though, is attempt to identify what "kind" of rock or mineral it was that you just threw.

Minerals

A mineral, in the geological sense, is a substance that possesses the following characteristics: naturally occurring, inorganic, solid, definite chemical composition, and has an ordered internal structure.

• Naturally occurring means that people did not make it. Steel and aluminum are alloys, and plastic and rubber are polymers. While each of them are created using natural materials, they do not exist that way in nature. They are synthetic or artificial.
• Inorganic means that it was not made by a living thing. A pearl is naturally occurring but it was made by a living clam; wood is also naturally occurring but it was at one time a living tree. Wood and pearls are not minerals.
• Solid means that it is not a liquid or a gas at standard temperature and pressure. Water is naturally occurring and inorganic but is a liquid; it is not a mineral.
• Definite chemical composition. This is less clear than the above examples but just means that the mineral has an identifiable chemical make-up. For example, say you have two rocks that look very similar in appearance. We might be tempted to label them the same kind of rock and move on. But if we examine their chemical formula, we might find out one is calcite and the other is limestone. This can be an important distinction in geology depending on what you're looking for and what you want to do.
• Ordered internal structure. Like with chemistry this is not something you can see when you look at a mineral but describes it's atomic structure, it's atoms, at a microscopic level.

This sounds very technical and precise, and we might be tempted to flatter ourselves that with a bit of time we can memorize these details and soon be able to call ourselves geologists. But not so fast. These minerals have nothing to do with the one-a-day vitamins we may have taken at breakfast-time this morning. Some rocks were created from prehistoric organisms that were very much alive at one time. And in mining, some geologists consider anything obtained from the ground and used by people is considered to be a "mineral commodity" or a "mineral material." And we haven't even talked about rocks yet!

Rocks

A rock (or stone), in the geological sense, is a natural substance, and it is a solid aggregate of one or more minerals. Classifying rocks is challenging since there is much overlap in the composition of the different kinds, so geologists organize the study of rocks by how they were formed. There are three major types of rocks: igneous, sedimentary, and metamorphic.

• Igneous rocks are formed from the solidification of molten rock (magma or lava). There are two basic types:
  • Intrusive or plutonic igneous rocks, such as granite, result when magma cools and crystallizes below the earth's surface, and the slow cooling that occurs there allows large crystals to form.
  • Extrusive or volcanic igneous rocks, such as basalt, erupt onto the earth's surface, where lava cools quickly to form small crystals. Some cool so quickly that they have a glass-like appearance.
• Sedimentary rocks are formed at the earth's surface by the accumulation and cementation of fragments of earlier rocks, minerals, and organisms, or as chemical precipitates, and organic growths in water. There are three basic types of sedimentary rocks.
  • Clastic sedimentary rocks, such as shale and sandstone, are formed from mechanical weathering debris of other rocks (erosion).
  • Chemical sedimentary rocks, such as dolomite, form when dissolved materials precipitate from solution (evaporite).
  • Organic sedimentary rocks, such as coal, form from the accumulation of plant or animal debris (detritus).
  Regardless of the source of the sediment, the particulate matter then undergoes compaction and cementation (diagenesis).
• Metamorphic rocks began as Igneous or Sedimentary rocks but have been modified by heat and pressure, after it was originally formed, and usually while it's still buried deep below earth's surface. Exposure to these extreme conditions alters the mineralogy, texture, and chemical composition of the rocks. Metamorphism means change in form. There are two basic types of metamorphic rocks:
  • Foliated metamorphic rocks, such as slate, have a layered or banded appearance that is produced by exposure to heat and pressure.
  • Non-foliated metamorphic rocks, such as marble, do not have a layered or banded appearance.

The Rock Cycle

The Rock Cycle. The really interesting thing about rocks is that they don't stay the same but they actually change all the time, believe it or not, from one type of rock to another. Of course, this change is a very slow process and takes place over millions of years. The thought of rocks transforming themselves into other types might sound odd but the process is simple to understand. For example, magma might turn into an intrusive igneous rock which is forced to the surface by a volcano where it becomes an extrusive rock which is then weathered and eroded into particles which settle somewhere on the earth's surface or the ocean floor where it becomes a sedimentary rock which is metamorphized into yet another type of rock and perhaps by a shift in the earth's tectonic plates it is driven underground where heat and pressure turn it back into magma and the cycle begins again.

The Science of Rocks

Petrology is the general branch of geology that studies the origin, composition, distribution and structure of rocks.

Example. The specimen rock is sedimentary in nature. It is dolostone with traces of iron ore and sandstone mixed into its mass. The sedimentary layers combined with its current altitude above sea level indicate it was formed as part of the Sydney basin but was subsequently lifted to its current elevation during (i.e., it predates) the tectonic displacement that gave rise to the Great Dividing Range over 300 million years ago.

Petrography is the specialized branch of geology concerned with the description and classification of rocks with "microscopic" detail. This takes place mostly in the laboratory.

Example. CaMg(CO3)2

Lithology is the speciality which focuses on the "macroscopic" description of rocks. It is a description of a rock's physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy (a magnifying glass). This involves such things as colour, texture, grain size, or composition. It may be either a detailed description of these characteristics or be a summary of the gross physical character of a rock.

Detailed example. The specimen rock is predominantly light gray in color but includes traces of rusty red and light tan to medium brown. The grains are fine for each variety of rock included and has an overall smooth and even texture due to weathering.

Summary example. Round and flat, approximately 3-4 meters in diameter. It looks like a giant damper bread.

Note. The examples provided are not intended to be encyclopedic or exhaustive but rather are intended to briefly illustrate each concept.

The posted coordinates will take you to the Box Vale Lookout where you will find, of all things, a rock. In fact, it is the rock that is described above in the section "The Science of Rocks".

To claim this cache:

1. Describe another feature of the rock that is not already mentioned in The Science of Rocks above.

2. Is your description petrologic, petrographic, or lithologic?

Please send your answers to me via the geocaching website - e-mail or message. The answers to these questions should not be included in your log, nor should your log include spoiler photos. You do not need to wait for a reply from me to log your find.