We have gathered some useful information below that will help you identify the rock, please read and consider each section, not all sections will be applicable, you may also like to use a search engine to do some extra reading to help with identification, be warned though, not everything you read on the internet is correct.
By definition Geology is an earth science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which they change. Geology can also refer generally to the study of the solid features of any celestial body.
Geology gives insight into the history of the Earth by providing the primary evidence for plate tectonics, the evolutionary history of life, and past climates. Geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, and for providing insights into past climate change. Geology also plays a role in geotechnical engineering and is a major academic discipline.
Geologists define a rock as:
A bound aggregate of minerals, mineraloids, or fragments of other rocks.
The use of the word 'bound' means that a rock must have structural integrity, e.g. an aggregate of sand does not become a rock until the grains are bound together. Typical binding agents are very fine grained minerals (e.g. calcite, clay) or mineraloids (e.g. chert, glass), though in some rock types the crystals are intergrown and no binder is required.
Generally speaking there are three main classes of rock, today we have added a fourth as we felt it appropriate for your trial as a Geologist.
Igneous Rocks: all form by the cooling of molten material known as magma. This can occur at or near the surface, at shallow depths in the earth’s crust, or deep in the crust.
Igneous rocks which form at or very close to the earth’s surface are called volcanic rocks. They generally have small sized or indiscernible crystals or glassy textures. Their classification depends on the chemistry of the rock, importantly the amount of silicon dioxide in the rock. Examples of volcanic rocks are basalt, rhyolite and obsidian.
Igneous rocks which form at shallow depths in the earth are known as hypabyssal rocks. They generally have smaller crystals. Examples of hyabyssal rocks include dolerite, microgranite and microdiorite.
Igneous rocks which cool and solidify deep in the earths crust are called plutonic rocks. Examples of plutonic rocks are granite, gabbro, and granodiorite.
In general igneous rocks are named depending on their minerals and hence chemistry. Those with a high proportion of silicon dioxide are known as felsic, those with an intermediate amount of silica are called intermediate and those with lower amounts of silica are called mafic. A fourth group very low in silica is called ultramafic. A formal classification scheme for igneous rocks is defined by the International Union of Geological Sciences.
There are a group of rocks, which fall halfway between volcanic rocks and sedimentary rocks. These rocks are the products of volcanic explosive activity and are called pyroclastic and volcaniclastic rocks. These include tuff, ignimbrites, and volcanic ash.
Sedimentary Rocks are rocks formed from the accumulation of sediment on the earth’s surface or the chemical precipitation of minerals on or near the surface.
Sedimentary rocks are divided into:
Clastic rocks made up of the fragments of weathered and eroded pieces of pre-existing rocks. Examples of this are sandstone, claystone, and conglomerate
Biogenic rocks formed from the accumulation of animal or plant remains. Examples are coal and limestone.
Chemical precipitates which form by the deposition of chemicals near or on the earth’s surface. Examples are bauxite, silcrete and ironstone.
Metamorphic rocks form by the alteration of pre-existing rocks by pressure and or heat in the crust. The rock is changed in solid state, with the heat and pressure changing the minerals in the rock. The rocks reflect the amounts of heat and pressure and the original material present. Metamorphic rocks are classified according to their fabric (rock texture) and their mineralogy.
Examples of metamorphic rocks are marble, schist, phyllite, quartzite, slate, amphibolite and gneiss.
By examining the mineral species present in a metamorphic rock, geologists can tell the pressures and temperatures at which it formed. Thus geologists can determine at what depth the rock has been buried prior to uplift.
Extraterrestrial rocks: Meteorites. A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the Earth's atmosphere and impact with the Earth's surface. When the object enters the atmosphere, various factors like friction, pressure, and chemical interactions with the atmospheric gases cause it to heat up and radiate that energy. It then becomes a meteor and forms a fireball, also known as a shooting/falling star; astronomers call the brightest examples "bolides." Meteorites that survive atmospheric entry and impact vary greatly in size. For geologists, a bolide is a meteorite large enough to create a crater.
Each of these rock groups contains many different types of rock, and each can be identified from its physical features.
Being able to describe and name rocks is one of the fundamental skills of a geologist. Important information regarding the nature of rocks is communicated through concise, accurate descriptions. This information allows the geologist to identify the rock, and, in the process, to learn about its history and the geological environment in which it was formed.
Knowledge of field relationships between different rock units is fundamental to the study of rocks. It is gained from mapping and observing rocks in the field.
Other useful information:
Legend Rock Metung: The Legend Rock, is an important part of Gunaikurnai mythology, it lies in shallow water by the shore of Bancroft Bay, opposite the Metung Yacht Club in Tatungooloong Country.
According to the legend; One day, some fisherman who had hauled in many fish with their nets, ate their catch around their campfire. The women, guardians of the social law, saw that the men had eaten more than enough but had not fed their dogs. As a punishment for their greed the fishermen were turned to stone.
This story is one of many Gunaikurnai stories that were told and retold to show that greed would bring punishment. The Legend Rocks hold great spiritual value to the Gunaikurnai people and the story serves as a great legend for its people to remember the laws of the land.
There were originally three rocks in the formation at Metung, unfortunately two were destroyed during road construction along the shore of Bancroft Bay in the 1960s. The last rock was preserved when community members and Gippsland & East Gippsland Aboriginal Cooperative had an injuction issued. The Legend Rock continues to be protected under the Heritage Act of Victoria.
A glacial erratic is a piece of rock that differs from the size and type of rock native to the area in which it rests. "Erratics" take their name from the Latin word errare, and are carried by glacial ice, often over distances of hundreds of kilometres. Erratics can range in size from pebbles to large boulders. Geologists identify erratics by studying the rocks surrounding the position of the erratic and the composition of the erratic itself. They can be transported by glaciers, they can be transported by ice rafting and they can be dropped by icebergs melting.
Weathering is the breaking down of rocks, soil and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters. Weathering occurs in situ, roughly translated to: "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity and then being transported and deposited in other locations.
Two important classifications of weathering processes exist – physical and chemical weathering; each sometimes involves a biological component. Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. The second classification, chemical weathering, involves the direct effect of atmospheric chemicals or biologically produced chemicals also known as biological weathering in the breakdown of rocks, soils and minerals.
In earth science, erosion is the action of surface processes (such as water flow or wind) that remove soil, rock, or dissolved material from one location on the Earth's crust, then transport it away to another location. The particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by its dissolving into a solvent (typically water), followed by the flow away of that solution. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres.
Natural rates of erosion are controlled by the action of geomorphic drivers, such as rainfall; bedrock wear in rivers; coastal erosion by the sea and waves; glacial plucking, abrasion, and scour; areal flooding; wind abrasion;groundwater processes; and mass movement processes in steep landscapes like landslides and debris flows. The rates at which such processes act control how fast a surface is eroded. Typically, physical erosion proceeds fastest on steeply sloping surfaces, and rates may also be sensitive to some climatically-controlled properties including amounts of water supplied (e.g., by rain), storminess, wind speed, wave fetch, or atmospheric temperature (especially for some ice-related processes). Feedbacks are also possible between rates of erosion and the amount of eroded material that is already carried by, for example, a river or glacier.
Petrifaction, or petrification as defined as turning people to stone, is also a common theme in folklore and mythology, In geology, petrifaction or petrification is the process by which organic material is converted into a fossil through the replacement of the original material and the filling of the original pore spaces with minerals. Petrified wood is a common result of this process, but all organisms, from bacteria to vertebrates, can be petrified (although harder, more durable matter such as bone, beaks, and shells survive the process better than softer remains such as muscle tissue, feathers, or skin). Petrification takes place through a combination of two similar processes: permineralization and replacement. These processes create replicas of the original specimen that are similar down to the microscopic level, and require a minimum of about 10,000 years to take place.
To successfully log this cache please observe Legend Rock, use your own judgment, the information provided and if required some internet research to answer the following questions. Send us your answers to the best of your ability;
1. What Group do you put Legend rock in to; Igneous, Sedimentary, Metamorphic or Extraterrestrial?
2. What were the factors that that led you to this choice?
3.How did Legend Rock come to rest where it is today?
4. A photo of your team, GPS near GZ with your log and answers. (optional)
You are welcome to log your answers straight away to keep your TB's and Stats in order but please message us with your answers within 24 hours. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted.
Source: Wikipedia, Geology.com, Queensland Museum.
