Archive for the 'Slate geology' Category...
Filed under Slate geology, Slate mining history, Slate quarrying methodologies
Honister is a unique award winning experience and England’s last remaining working slate mine.
Located at the head of the Honister Pass in the centre of the Lake District, this mine produces the world famous Westmorland Green slate – a beautiful, functional material that has been extracted here for centuries. This slate is 400 million years old!
Within the visitor centre, you’ll find a wealth of activities, attractions and information. Guided underground tours can also be arranged. They have live displays of traditional slate processing skills which provide a fascinating insight into the region’s industrial heritage.
Honister is owned by a local family and is a supporter of the Lake District community, economy and the environment. To visit their website, click on the image below:
Filed under Slate geology
Click here for a rock picture gallery from About.com. The list shows 60 different stones under the classifications of Igneous, Sedimentary, Metamorphic and ‘Other’. ‘Other’ refers to some pretty specialized rocks such as Fulgurite and Thunder Egg.
If you want to skip straight to the slate entry, click here.
Filed under Slate geology
500 million years ago, towards the end of the period when slate was formed, life suddenly became more complex and diverse. This period, named the ‘Cambrian explosion’ is of immense scientific interest and was an important moment in the history of life on Earth.
This proliferation of life is dubbed the ‘Cambrian Explosion’ because of the relatively brief time span of radical evolutionary experimentation when many major animal groups first began to appear.
Normally, only hard parts of ancient animals became fossilized - the bones, teeth and shells. Soft parts of creatures were rarely preserved, so the simple plants and invertebrate animals that had evolved during the period of slate formation (450 to 600 million years ago) left little trace in the fossil record.
Studies suggest that massive upheavals in the earth’s crust initiated a kind of reverse-greenhouse effect 500 million years ago that cooled the world’s oceans, spawned giant plankton blooms, and sent huge volumes of oxygen into the atmosphere. This event may have helped trigger the most massive growth of biodiversity in Earth’s history.
The image above is of Sanctacaris uncata that evolved during the Cambrian Period. These grew to around 4” in length.
Filed under Slate geology, Slate mining history, Slate photo of the week, Slate quarrying methodologies
A single slate wagon axle, showing the double flange and floating wheels that allowed wagons to negotiate uneven track.
Photo & words by kind permission of simonrl of www.aditnow.co.uk
Filed under Slate geology, Slate photo of the week, Slate quarrying methodologies
I was recently sent this stunning photo of a slate open quarry in China. The image has not been rotated! Look at the workers who are standing – they are vertical!
This photo dramatically shows the angle of dipping of the slate vein, dictating this particular method of extraction.
Open quarries follow the vein on the slope of the mountain and use this gallery mining system. It is not at all uncommon to find examples of more than one method of extraction within the same quarry. Click here for a previous post which explains these methodologies in more detail.
Filed under Slate geology, Slate mining history, Slate processing techniques, Slate quarrying methodologies
Mining has given rise to potentially hundreds of terms for processes, techniques and equipment. Many of these terms vary by region or were specific to the type of mine.
Click here for a comprehensive dictionary of mining terms from AditNow.
Link and words by kind permission of simonrl of www.aditnow.co.uk
Filed under Slate geology, Slate photo of the week
Yes, yes, I have used this photo before in my January 15th post entitled: How old is slate? but figured that some of you may not have looked back that far in my blog.
This is such a dramatic photo of Raja Multi Indian slate tile. The texture and colours are quite remarkable.
Filed under Slate geology
Slate is a metamorphic rock, formed under great pressure from what was originally mudstone. Its origins in Wales date back to the Paleozoic age between 350 and 500 million years ago. There are three types of slate found in Wales - Silurian, Ordovician and Cambrian.
Silurian is the most recent and is found in the Llangollen, Glyn Ceiriog and Corwen areas. It is not particularly durable but the industry in those parts developed because of its closeness to major markets. Its lack of durability is noticeable in the waste heaps which have turned back to shale in some cases.
Ordovician slate is found around Blaenau Ffestiniog and Corris, it is generally mined underground. It is almost uniformly blue-grey and is easily split using machines.
Cambrian is the oldest type and found in the north around Bethesda, Llanberis and in the NantlleValley. The colour is variable with a tendency towards purple, slates of this type are still mainly split and dressed by hand although there has been some success with mechanisation.
Words and photo by kind permission of Dave Sallery. For more information from his tremendous website, please click here.
Filed under Slate geology
Rocks are classified by mineral and chemical composition, by the texture of the constituent particles and by the processes that formed them. These indicators separate rocks into igneous, sedimentary and metamorphic. They may also be classified according to particle size, in the case of conglomerates and breccias or in the case of individual stones. The transformation of one rock type to another is described by the geological model called the rock cycle.
Igneous rocks are formed when molten magma cools and are divided into two main categories: plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earth’s crust (example granite), while volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta (examples pumice and basalt).
Sedimentary rocks are formed by deposition of either clastic sediments, organic matter, or chemical precipitates (evaporites), followed by compaction of the particulate matter and cementation during diagenesis. Sedimentary rocks form at or near the Earth’s surface. Mud rocks comprise 65% (mudstone, shale and siltstone); sandstones 20 to 25% and carbonate rocks 10 to 15% (limestone and dolostone).
Metamorphic rocks are formed by subjecting any rock type (including previously-formed metamorphic rock) to different temperature and pressure conditions than those in which the original rock was formed. These temperatures and pressures are always higher than those at the Earth’s surface and must be sufficiently high so as to change the original minerals into other mineral types or else into other forms of the same minerals (e.g. by recrystallisation). There are also Foliated and nonfoliated rock types.
The three classes of rocks: the igneous, the sedimentary and the metamorphic — are subdivided into many groups. There are, however, no hard and fast boundaries between allied rocks. By increase or diminution in the proportions of their constituent minerals they pass by every gradation into one another, the distinctive structures also of one kind of rock may often be traced gradually merging into those of another. Hence the definitions adopted in establishing rock nomenclature merely correspond to selected points (more or less arbitrary) in a continuously graduated series. This is frequently urged as a reason for reducing rock classification to its simplest possible terms, and using only a few generalized rock designations. But it is clear that many apparently trivial differences tend regularly to recur, and have a real significance, and so long as any variation can be shown to be of this nature it deserves recognition.
Filed under Slate geology
It is theorized that all of the Earth’s land masses were once joined together in a single continent known as ‘Pangaea’ which, around 180 million years ago, split in two - Laurasia in the north and Gondwanaland in the south. As time (a lot of it!) passed, these two land masses split apart several more times into the continents we now know. When one considers that the slate deposits that run up the east coast of North America are virtually identical to those found in Wales, it seems like a plausible explanation.
The former existence of a single ‘supercontinent’ was proposed by German meteorologist Alfred Wegener in 1912.
Click here to see a full size image of the above globe.
