This is a multi theme earthcache. Taking you to the statue of Mr Wilder, the statue that has been called a geological wonder. Incorporating beautifully colourful and exotic rock types that are the themes of this earthcache!
In Irish Gaelic: Grian Cloch, means 'stone of the sun.
The learning point of this earthcache theme is to get the geocacher to become familiar with the mineral quartz. It is the most widely distributed mineral found on the Earth's surface. The boulder Wilde reclining on is a 35 tonne block of vein quartz the sculptor hand picked in Ireland’s Wicklow Mountains where it had weathered out of a vein in the Leinster Granit.
Quartz is a chemical compound consisting of one part silicon and two parts oxygen. It is silicon dioxide (SiO2). It is the most abundant mineral found at Earth's surface, and its unique properties make it one of the most useful natural substances.
It is present and plentiful in all parts of the world. It forms at all temperatures. It is abundant in igneous, metamorphic, and sedimentary rocks. It is highly resistant to both mechanical and chemical weathering. This durability makes it the dominant mineral of mountaintops and the primary constituent of beach, river, and desert sand. Quartz is ubiquitous, plentiful and durable. Minable deposits are found throughout the world.
Quartz occurs in two basic forms:
1. The more common macrocrystalline quartz is made of visible crystals or grains. Examples are rock crystals, the grains in sandstone, but also massive quartz that is made of large crystallites without any crystal faces, like vein quartz.
2. Cryptocrystalline quartz or microcrystalline quartz is made of dense and compact aggregates of microscopic quartz crystals and crystallites. Examples are agate and chert. The different types of cryptocrystalline quartz are colloquially subsumed under the term chalcedony, although that term has a more strict definition in scientific literature. It is worth mentioning that most chalcedony contains small amounts of another SiO2 polymorph, moganite, so it is not always pure quartz.
Quartz use, and excellent as a gemstone?
Quartz is one of the most useful natural materials. Its usefulness can be linked to its physical and chemical properties. It has a hardness of seven on the Mohs Scale which makes it very durable. It is chemically inert in contact with most substances. It has electrical properties and heat resistance that make it valuable in electronic products. Its luster, color, and diaphaneity make it useful as a gemstone and also in the making of glass.
As a gemstone it is hard, durable, and usually accepts a brilliant polish. Popular varieties of quartz that are widely used as gems include: amethyst, citrine, rose quartz, and aventurine. Agate and jasper are also varieties of quartz with a microcrystalline structure.
The learning point of this earthcache theme is to get the geocacher to become familiar with the mineral thulite. The pink national stone of Norway.
Thulite, also known as Roselite is well-known in Norway, where it was first found. It is named after the mythical region of Thule, which many identify with Norway. Notable occurrences are also to be find in the Austrian Tyrol, Western Australia, Russia and in the USA. The color of Thulite is caused by the element manganese in its composition. Thulite often occurs associated with Quartz, and is often mottled with streaks or spots of white Quartz.
In the mineralogical literature, Thulite is often called pink Zoisite, as it is in fact a pink version of the mineral, rich in manganese. Molten together with White calcite, Thulite is often found in the fractures of many rocks. Its hardness is somewhat lower than the hardness of Quartz, but still pretty solid for jewelry production. It is a non-magnetic and non-fluorescent mineral.
Clinothulite is pink, manganese-rich variety of the mineral Clinozoisite. Zoisite and Clinozoisite are very similar minerals, differing only in crystal structure. This makes Thulite and Clinothulite almost identical, and sometimes it is impossible to make a distinction without complex tests.
Thulite is an inexpensive gemstone. It is cut into cabochon and beads, and carved into ornamental objects. The color of Thulite can range from pink to dark red. It can be polished to a high gloss. As this gem is opaque in appearance, it is most often shaped into cabochons or carved as small, ornamental objects.
Facts about Thulite:
Chemical formula: Ca2Al3(SiO4)3(OH)
Color: Red, Pink
Hardness Mohs scale: 6 – 6.5
Crystal system: Orthorhombic
Mineral class: Zoisite
Transparency: Opaque. May be translucent in thin backlit sections.
Thulite can sometimes be confused with rhodonite. Generally, rhodonite is darker and is sometimes included with dark minerals. Surface oxidation can also alter the color of this material, providing a brown tint.
Rhodochrosite is another stone that is sometimes mistaken for thulite. The distinctive banding of rhodochrosite makes it easily distinguishable from thulite, however.
The little village and area of Sauland is well known for being the area where thulite was first discovered. It's located in a county of Telemark, Norway. A place with rock croppings and valleys that make the land and area difficult to navigate. But it was nearly two hundred years ago, the stone was dug up near the presents of Øvstebø and Kleppan farms. Anders Gustaf Ekeberg, a Swedish chemist, is credited with its discovery.
Besides the production of thulite, Sauland is also the home to cyprine. Cyprine is a blue variety of vesuvianite, owing its color to the presence of copper.
Its gone 200years from it first was found in this area now, but during modern times, Norway is still the primary producer of thulite. Most material is sourced from Tvedestrand and Leksvik in south of Norway, Aust-Agder. They are located to the southwest of Sauland, Telemark.
The learning point of this earthcache theme is to get the geocacher to become familiar with the rock Larvikite. The color mixed rock with large crystals that shines like no other rock, and it origin from Telemark, Norway.
Larvikite is a rare pluton rock species (monzonite) found in the norwegian states of Vestfold and Telemark. These rocks were formed around 290 million years ago in connection with the volcanic activity in what the geologists calls the Oslo field.
Almost 90 percent of the larvikite consists of feldspar, and the crystals are composed in such way that the blue color makes up a blue color mix when the light is broken into the tiny lamellas inside them.
We call this optical phenomenon for the "Schiller effect". This is because of the very special composition of the feldspar in the stone. If we put a larvikite sample under a microscope we can see these lamellas very clearly. The color mix only appears where they are particularly close to each other, while we will not be able to see this if the distance between the lamellas are within a longer distance of each other.
The larvikite also contain small amounts of darker minerals, such as amphibol, olivine and biotite, and the most attractive variants lead to small amounts of the mineral nephelin. In modern geological nomenclature, larvikite classifies as monzonite.
The Larvikite quarries.
Large blocks of larvikite, up to 30 tons, are taken out of the quarries round the areas of Larvik, Norway.
Several types of larvikite are taken out from the quarries. At Tvedalen west of Larvik that is the largest operating area, this is where the light blue larvikite ("Blue Pearl" or "Lundh's blue") is taken out. The dark larvikite (Emerald Pearl "or" Lundh's Emerald ") is to find east of Larvik in Tjølling. There are also two medium-light larvikite types ("Marina Pearl "or" Lundh's Marina "and" Lundh's Ocean "). In the north western part of larvik, at Malerød, a lighter type with larger crystals ("Lundh's Royal") is found. In earlier days, several other types were produced, including red-brown (oxidized larvikite without the color mix) at Tønsberg and at Bolærne, and a greener type out at Nøtterøy.
The way larvikite is made.
Larvikite is a melted rock (magmatic rock), and was made in the depths, about 30 kilometers down. When the melt was cooled down and solidified, large crystals were formed. This occurred in early days, 300-200 million years ago in connection with the breakup of the super continent Pangea, and then the formation of the Oslo Field. The solid rock was raised up to the surface during a various of geological processes. Conditions inside earth and up on the surface are very different, so the crystals that were once formed are no longer stable. There has now been a microscopic change in the feldspar mineral, and this has created the blue color mix that we today can observe in the larvekite.
The learning point of this earthcache theme is to get the geocacher to become familiar with the rock charnockite. This is a very special stone that is not found everywhere, but the species is a wonderful colored stone that comes in lovely different colors.
Charnockite has an interesting name, and it has also an interesting origin. It was given to the rock type because it was first described as a tombstone of Job Charnock (1630–1692) in St John’s Churchyard in Calcutta (Kolkata), India. Job Charnock is known as the founder of the same city. Even today charnockite remains to be popular as a tombstone material, but you don’t hear the name used too often.
The lovely species that you can see here at gz origin from India, and is a black Indian charnockite sample. So let’s get to know more about this “mystic” rock:
Fig 1: Detailed geological map of the charnockitic zones adjacent to the Munster Suite at Palm Beach.
Fig 2: Locality map of Margate Terrane showing the distribution of Munster Suite and other charnockite varieties including the Oribi Gorge Suite and the Margate Granite thermal aureoles and fluid gradient charnockites. Also shown are the locations of detailed maps shown in Figs. 7 and 10. Note also the location of Marble Delta as well as the quarry location where fluid-driven charnockites are exposed.
Charnockite is a granofels that is formed at high temperature and pressure, and contains *orthopyroxene, quartz, and feldspar. Being composed mainly by quartz, perthite or antiperthite and orthopyroxene. Charnockite is frequently described as an orthopyroxene granite. Granites are felsic rocks that usually contain no or very little pyroxene. There is actually an entire array of rocks that may contain orthopyroxene plus quartz. These rocks are collectively referred to as charnockitic rocks or charnockitic suite. All of these rock names refer to igneous rocks which makes it very logical to assume that charnockite is just an igneous rock with a somewhat unusual composition.
*(Orthopyroxene, any of a series of common silicate minerals in the pyroxene family. Orthopyroxenes typically occur as fibrous or lamellar (thin-plated) green masses in igneous and metamorphic rocks and in meteorites.)
Charnockites are found in high-grade metamorphic terranes (granulite facies). The transformation from the protolith to charnockite had probably no magma phase, which means that in most cases we are dealing with true ***metamorphic rocks which have nothing to do with the **igneous processes. Charnockitic rocks are sometimes described as granulites, but this term seems not to be very often used now a days. Most because it may and can be confused with metamorphic facies with the same name.
** (Igneous rocks: Igneous rocks are formed by the solidification of magma, a silicate liquid generated by partial melting of the upper mantle or the lower crust. Different environments of formation, and the cooling rates associated with these, create very different textures and define the two major groupings within igneous rocks.)
*** (Metamorphic rocks : These rocks get their name from the Greek words ‘meta’ and ‘morph’, meaning ‘change of form’. Metamorphic rocks are produced by the alteration of pre-formed rocks by pressure, temperature and migrating fluids, often in environments deep in the Earth’s crust. Because of the severe conditions which rocks undergo during metamorphism, the original minerals may become unstable and change to maintain equilibrium with the new environment. This can involve changes in mineralogy (recrystallization of existing minerals or formation of new ones) and usually changes in texture from the original rock.)
So is it a granite stone? The conclusion is no as the term “granite” isn’t reserved exclusively for igneous rocks. Some rocks that have been described as granites are almost certainly metamorphic rocks, although they lack obvious foliation. We have to tolerate the situation that not all granites are igneous rocks and therefore we have no basis to demand that charnockite shouldn’t be named granite anymore. However, if we want to use metamorphic terminology, then we should call it granofels. Charnockite is coarse-grained, and it lacks foliation. This is the definition of granofelsic metamorphic rocks.
The Charnockitic rocks are commonly green. Both feldspars and orthopyroxene tend to have a greenish or brown hue and quartz crystals may contain rutile needles which gives them bluish tinge. Charnockites are formed at high pressures in almost water-free conditions. That’s why we see only small amounts of hydrous phases here (biotite, amphiboles) which are widespread in the rocks of amphibolite facies. So the Charnockites have a granitic composition according to the QAPF classification (see diagram), but only because we do not use pyroxenes in this classification scheme.
QAPF diagrams are mostly used to classify plutonic rocks (phaneritic rocks).
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1. Answer the questions under by visiting the Coordinates.
A. Now that you have been through all the themes above, place the stone / minerals to the correct clothing / place. # The trousers = , # The shoes = , # The boulder = , # The Collar & sleeve = .
B. Is the Charnockite rock: very fine-grained, fine-grained, medium-grained, coarse-grained, large-grained?
C. A-1) Nearly 90% of the larvikite consist by what mineral? A-2) What is so different with this mineral in this type of stone? Describe the phenomenon!
D. Study the quartz you see at gz! Is it cryptocrystalline quartz or macrocrystalline quartz that you see?
E. Describe the Thulite that you see! What colors can be seen in it? And is the thulite randomly built up? By that I mean: crystals or folded lines, or both?
2. (It’s voluntary to post a photo in your online log of your visit)
Without revealing any answers!