The geology of the local area is one defined by limestone, indeed the Romans called it Calcaria (place of limestone). There are different types of limestone, though what we have come to examine is an example of Magnesian Limestone. Limestone is a sedimentary rock.
Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle in place. The particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, the sediment was formed by weathering and erosion from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers. Sedimentation may also occur as minerals precipitate from water solution or shells of aquatic creatures settle out of suspension.
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3). Most limestone is composed of skeletal fragments of marine organisms such as coral, crinoids and molluscs.
The stone used here, is a different type of limestone. It is known as Magnesian Limestone CaMg(CO3)₂, often called Dolomite, was originally formed in the shallow tropical Zechstein sea some 250 million years ago. It has subtle colour variations from white to pale yellow, and is an oolitic limestone. Oolitic limestone is a carbonate rock made up mostly of ooliths (or ooids) which are sand-sized carbonate particles that have concentric rings of Calcium Carbonate. These rings are formed around grains of sand or shell fragments that were rolled around on the shallow sea floor, gathering layer after layer of limestone.This limestone formed in a shallow sea. The rock has an even structure rather like cod roe and it can therefore be cut or sculpted in any direction. This feature, coupled with hardness, colour and durability, gives the limestone its quality as a building stone. Its colour can be white, grey or yellow, with a fine grained texture.
There are many EarthCaches that discuss limestone in greater detail, what we have come to see and learn about are Vugs.
So what is a Vug?
A Vug is a small to medium sized cavity inside a rock. Commonly they can be filled or partially filled by quartz, calcite or other minerals. More rounded crystal lined cavities in sedimentary and igneous rocks are known as Geodes. They can be caused by air or gas bubbles, and once the rock hardens around the cavity, then minerals that form part of the rock, through the process of deposition line the inside surface, over time crystals form. As a vug or geode form part of the structure of the rock, they may not be normally seen, but as the rocks are weathered and eroded they then become apparent. If you want to learn about weathering and erosion there are plenty of EarthCaches which describe these processes.
Lets have a look for some Vugs.
Please have a look at the gateposts, there is no need to enter the church grounds, and this EarthCache can be done at any time of the day or night.
(1) First what does the stone forming the gatepost feel and look like?
(2) There are Vugs here, please describe them in terms of
(i) Their size in mm.
(ii) Their structure, are they rounded or irregular?
(iii) What is the internal structure of the Vug like, what can you see?
This being an EarthCache, in order to log it, I ask that you answer the above questions. Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile.