Castle Gardens is the most historically significant open space in Lisburn and was once the site of Lisburn Castle, a 17th century fortified manor house, built by the Conway family, the landlords of Lisburn. Upon the death of the last landlord, Sir Richard Wallace, and later his wife, Lady Wallace, the Gardens were gifted to the people of Lisburn by Lady Wallace’s heir, Sir John Murray Scott in 1903.
The upper 19th century gardens and the 17th century terraces were restored by Lisburn City Council, with grant aid from the Heritage Lottery Fund in June 2008. The World War II Air Raid shelter was also converted into an education centre, for school and community use as part of this restoration project.
We are here to look at different types of igneous stone at two locations.
At the posted coordinates you will find two different columns on the Wallace monument.
At stage 2 you will find a cannon on top of a stone plinth.
Logging Requirements (Questions to Answer)
In order to log a find against this EarthCache, you will need to visit GZ and make some observations and then answer some questions and send answers to me via my Geocaching profile or through the Messenger Centre.
1) Wallace Monument. Please describe the appearance and explain which of the three rocks the large outer columns are made of.
2) Wallace Monument. Please describe the appearance and explain which of the three rocks the small inner columns are made of.
3) Stage 2. Please describe the appearance and explain which of the three rocks the plinth is made of.
4) Of the three, which one contains Potassium Feldspar
5) Given your answers above and the information below, would you say the granite's are Intrusive or Extrusive?
6) Compulsory task: Include in your log a photograph of you, your GPS or another identifiable item near GZ, taking care not to include anything in the photo that may give away your answers.
Granite.
Igneous and sedimentary rocks differ significantly in their formation processes and hardness. Igneous rocks originate from the cooling and solidification of molten magma or lava. This process, either deep within the Earth's crust (intrusive) or on its surface (extrusive), results in the formation of crystals, giving igneous rocks a generally hard and crystalline structure. On the other hand, sedimentary rocks are formed through the accumulation and cementation of sediments, such as mineral and organic particles, over time. These sediments are often derived from the weathering and erosion of pre-existing rocks. Due to their formation from loosely compacted materials, sedimentary rocks are typically softer compared to igneous rocks. The contrasting processes of solidification from molten material versus sediment compaction contribute to the distinct textures and hardness levels observed in these two major rock types.
What is an Igneous Rock?
An Igneous rock is formed by the cooling of Molten rock. Igneous rock comes in two categories: 1. Intrusive and 2. Extrusive.
1. Intrusive Igneous rock occurs when the cooling of molten rock occurs under the Earth's surface. As it cools under the Earth's surface it cools slowly which enables large crystals to form. The slower the cooling the larger the crystals form.
2. Extrusive Igneous rock occurs when the molten rock cools on top of the Earth's surface. As the rock is exposed to the Earth's elements such as rain etc the rock cools quickly and if crystals form they are usually quite small. Often not visible to the naked eye.
Why are granite rocks different colours?
The relative ratio of different colored minerals in a granite is largely due to the original source of molten rock that cooled to form the granite. If the molten rock was abundant in potassium feldspar, the granite is more likely to take on a salmon pink colour. On the other hand, if the molten rock is abundant in quartz and some other minerals one may get a black and white speckled granite.
Below are some components of Granite and their colours:
- Quartz - typically milky white colour
- Feldspar - typically off-white colour
- Potassium Feldspar - typically salmon pink colour
- Biotite - typically black or dark brown colour
- Muscovite - typically metallic gold or yellow colour
- Amphibole - typically black or dark green colour
1. Granite:
Granite is a Crystalline (Contains crystals) igneous rock which is made mainly of Quartz, feldspar, mica and a small trace of other minerals. Granite has to be at least 20% quartz to be called Granite. Granite is typically: 20-60% quartz, 10-65% feldspar, and 5-15% micas. The presence of orthoclase or plagioclase in granite depends on the specific geological conditions during its formation. Orthoclase feldspar is more commonly found in granites that solidify at higher temperatures in the Earth's crust. On the other hand, plagioclase feldspar is prevalent in granites that form at lower temperatures. These feldspar minerals contribute to the overall composition and appearance of granite, with orthoclase imparting a pinkish hue and plagioclase ranging from white to grey.
2. Granodiorite:
Granodiorite is an igneous rock that falls between granite and diorite in terms of composition. It is classified as an intermediate rock due to its medium silica content. Primarily composed of plagioclase feldspar, quartz, and biotite or amphibole minerals. It lacks significant amounts of orthoclase or microcline feldspar, which distinguishes it from granite. Typically light to medium gray, with speckles of black or dark minerals such as biotite or hornblende. It has a medium to coarse-grained texture similar to granite. Granodiorite forms from the partial melting of basaltic rocks in the Earth's crust, resulting in an intermediate composition between felsic granite and mafic diorite. It is commonly found in volcanic arcs, island arcs, and continental margins.
3. Diorite:
Diorite is an intrusive igneous rock that is primarily composed of plagioclase feldspar and hornblende or pyroxene minerals. It is classified as a mafic rock due to its lower silica content compared to granite and granodiorite. It has a dark-colored appearance, ranging from dark gray to black, with speckles of white plagioclase feldspar crystals. It has a medium to coarse-grained texture, similar to that of granite and granodiorite. The mineral composition of diorite includes plagioclase feldspar (sodium-rich), hornblende, and pyroxene. Diorite forms from the slow cooling and crystallization of magma in the Earth's crust. It is less common than granite and granodiorite but is still used in construction and as a decorative stone. It is known for its durability and resistance to weathering.