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Biotite muscovite granite specimens from St. Austell in Cornwall, UK of Permian age is a coarse grained igneous rock composed of quartz, plagioclase feldspar, biotite and muscovite. The rock is part of the St. Austell pluton which formed 280 million years ago. An off white colour with gold and black flecks of micas, the rock has a unique chemistry and resulted in the rich mineralisation of ores in the area. The samples are suitable for collectors and educational use to show granite variants, available in three sizes. Each piece will come supplied in a card tray with an information label.
We also supply Biotite Muscovite Granite thin sections for microscope study which are available to buy HERE.
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Biotite muscovite granite is coarse grained rock and another variation of granite which is felsic in chemistry, meaning that its main constituent minerals are quartz and feldspar. The quartz has a white colouration which is down to the presence of fluid gases present during the formation of the rock which stop the quartz forming clear. Plagioclase, a potasium mineral being white in general due to either being albite or anorthite gives the rock an overall off white tone in colour. However, this rock also contains numerous biotite and muscovite mica crystals which both contrast in colour from one another due to differing chemistries. Muscovite, like all micas form in sheets and is often colourless when the sheets are single, however, when overlaid can give a bronze or brassy appearance with a hint of green. Biotite mica on the other hand, while almost identical in chemistry, also contains higher amount of iron (Fe), thus, the mineral appears black. All of these minerals together comprise of this rock which is better known as ‘Cornish Granite’. The granite however is part of the Cornubian batholith, specifically the St. Austell pluton, an igneous granitic body which formed during the Permian period around 280 million years ago and was the driving force behind various intrusions of heat and fluid infiltrating the local rock already in the area which resulted in mineralisation and later leading to rich ore deposits. The feldspar from exposed occurrences of this granite and others in the area eventually led to the formation of kalonite which would later be used to produce china clay. An excellent rock specimen for serious collectors as well as college or university level education, these particular rock samples can be used to both describe the variations that one may find in granites as well as show the chemistry of the rock and how such an igneous body can alter it’s surroundings and result in mineral ores being deposited. These samples come from St. Austell in Cornwall, UK and are available in three sizes and come supplied in a card tray with an information label.
We also supply Biotite Muscovite Granite thin sections for microscope study which are available to buy HERE.
Weight | 130 g |
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Specimen Size | 2" x 2", 3" x 2", 4" x 3" |
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An off white coloured streak plate made form porcelain, they are used by field geologists and students as a means of performing streak tests on minerals. This test simply involves one, scratching the surface of the tile with a particular rock or mineral, the coloured streak left behind then assists the user in determining the mineral, or minerals within a rock sample.
Accretionary lapilli tuff is an igneous pyroclastic rock, these samples come from Longsleddle, Cumbria in the UK and forms when hot ash and debris is ejected from as volcano. Some of this material is held together by moisture and once heavy enough, falls into the ash below forming small ‘spots’ within the material, creating a speckled rock. The samples are suitable both for young and serious collectors as well as educational use and are supplied in various sizes with a card tray and label.
65 in stock
Ignimbirte welded tuff is a pyroclastic rock of any origin formed through volcanic processes, the rock appears to show streaks of welded material on some surfaces and appears to be rhyolitic on the inside. Specimens come from Cumbria and are available in various sizes.
We also supply Welded Tuff thin sections for microscope study which are available to buy HERE.
72 in stock
Trachyte, a common igneous rock composed of various minerals including quartz, feldpsars, micas and olivine, rock specimens come from East Lothian, Scotland and are available in optional sizes, supplied in a card tray with a label.
Specimens of Basalt, collected from Northern Ireland. Basalt is a common, extrusive igneous rock, that forms when magma erupts and cools quickly on the Earth’s surface. These specimens are part of the Antrim lava group and date to the Tertiary period, around 60 million years ago. This is the same as the Basalt that makes up the famous Giant’s Causeway. The chemistry of these specimens suggests that the rock is olivine basalt, and comprises plagioclase feldspar, olivine and augite. These specimens are available in multiple sizes and come in a white card tray with an information label.
We also supply Basalt thin sections for microscope study which are available to buy HERE.
10 in stock
Biotite granite igneous rock specimens from Ballachulish, Scotland, UK. Composed of the felsic minerals quartz and feldspar, with occurrences of biotite crystals. The rock has an overall white appearance due to its felsic chemistry but the black biotite mica offers a striking contrast in colours. The samples are ideal for both collectors due to the attractive nature and for college to university level education to describe the variations in granite which one may find. The samples are available in three sizes and supplied in a card tray with an information label.
64 in stock
German Eclogite specimens from Weissenstein, Bavaria. Eclogite is a metamorphic rock, featuring red garnets within a matrix of sodium rich plagioclase called omphacite. These samples are perfect for both collectors and for educational use. They come supplied in a white card tray with an information label. Limited stock available.
Augite granophyre igneous rock specimens from Carrockfell, Keswick in Cumbria, UK. Excellent pieces exhibiting a medium grain size of crystals which constitute this rock including, augite, quartz and feldspars and shows a granophyric texture. Suitable for avid collectors and higher educational use, the samples come supplied in a sized card tray with an information label.
84 in stock
Amygdaloidal basalt is an igneous rock which is extrusive in nature, these specimens formed over 60 million years ago during the Tertiary period and come from Ireland. They are part of the Antrim lava group and exhibit a dark colouration with occurrences of amygdales containing quartz and calcite crystals. As a basalt they are somewhat dense, but lighter than pure samples due to the cavities within them which formed as a result of gaseous activity during their ejection. Over time, hydrothermal fluids pass through the rock and minerals form within the cavities, which gives the usually dark coloured rock a speckled appearance. These samples are available in various sizes and are suitable for higher educational use to detail the subtle differences between similar igneous rocks, they come supplied in a card tray with an information label.
58 in stock
Specimens of Ironstone that have been collected from Breitung Mine, Marquette County, Negaunee, Michigan, USA. These specimens are a deep reddish brown in colour with some specimens exhibiting clear banding. Please note that banding is not visible on all pieces. These specimens are available in very limited supply with three sizes to choose from. They come supplied in a white card tray with information label.
Additionally we also have one large display piece available, measuring approximately 18cm x 15cm at its widest points. This display specimen exhibits a distinct botryoidal texture on its top surface, making it an intriguing and appealing specimen to add to any collection.
Specimens of Rapakivi Granite sourced from South Finland, which have undergone cutting and polishing. This particular rock belongs to the Granite family, and shares the typical characteristics of granite. Those being a coarse-grained, plutonic igneous rock, consisting of orthoclase feldspar, quartz, and biotite mica. Each piece comes packaged in a white card tray accompanied by an information label.
Agglomerate igneous rock specimens from Scotland, UK. A coarse grained, hard blocky rock exhibiting a conglomeration of various minerals and igneous material of volcanic origin. These samples formed part of the Glen Coe caldera and are apart of the upper streaky andesite unit, the exhibit poor sorting and orientation of material which indicates a somewhat violent origin but this can vary from agglomerates by location and is mainly down to the chemistry of the igneous material. The samples are available in 3 sizes and come supplied in a card tray with a label, they are suitable for educational use to show the different types of volcanic rocks produced as well as those interested in collecting rock samples.
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