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An igneous rock exhibiting a porphyritic texture containing large cubic crystals of feldspar within a fine grained matrix. Collected near Oslo, Norway. Each sample is supplied in a labelled card tray. Each sample is supplied in a labelled card tray.
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Rhomb porphyry is an porphyritic alkaline syenite composed of an alkali feldspar groundmass with augites having rhombohedral cross sections as the principal phenocryst minerals. It is formed when a column of rising magma is cooled in two stages. The first deep in the crust creating the larger crystals with a diameter of 2mm or more. In the final stage at much shallower depths or during ejection from a volcano the cooling is rapid creating the much finer matrix. Traditionally the term “Porphyry” refers to the purple- red form of this stone prized in antiquity for it’s hardness & excellent building qualities particularly in Ancient Rome. This rock specimen is available in various optional sizes as well as in a 3″ size piece with a cut and lacquered face to detail the crystal structure of the rock in much clearer detail.
Weight | 130 g |
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Specimen Size | 2" x 2", 3" x 2", 4" x 3" |
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An igneous rock exhibiting a porphyritic texture containing large cubic crystals of feldspar within a fine grained matrix. Collected near Oslo, Norway. Each sample is supplied in a labelled card tray. Specimens are supplied in a polythene bag in lots of 1 kg with a label.
Rhomb porphyry thin section exhibiting the textbook porphyritic texture of this rare igneous rock. The thin section shows a fine grained alkali feldspar groundmass with large phenocrysts of augite. This material was collected near Oslo in Norway.
6 in stock
Mahogany obsidian sourced from the United States of America. Impurities of magnesium and iron give this variety a red or brown appearance hence the name ‘mahogany obsidian’ or oak obsidian. Each Sample is supplied in a labelled card tray.
Out of stock
Obsidian is an extrusive igneous rock, these specimens exhibit a typical black colouration with conchoidal fractures, they come from South East Mexico and are excellent for educational use and collectors due to the quality. This igneous rock forms when magma extrudes onto the earths surface, chemically it is silica rich and impurities give the black colouration. It’s fine crystalline texture and fracture makes obsidian appear glassy and it breaks as such. The pieces are available in various sizes and come supplied in a card tray with an information label.
Pumice specimens from the Lipari islands, Italy. Pumice is an igneous rock with a highly porous structure resulting from trapped gas bubbles as the lava was being ejected. The rock is usually very light & buoyant in water. Specimens are supplied in a card tray with label.
64 in stock
Olivine dolerite igneous rock specimens from Clee Hill, Shropshire, UK, composed of pyroxene minerals such as augite and magnetite as well as plagioclase feldspar. The samples are fine grained and crystalline in texture with a dense weight and black colouration. Similar in appearance to gabbro and basalt, the rock samples are suitable for serious collectors or higher level education to explain the difference in chemistry and mineralogy of igneous rocks. The samples are available in three sizes and supplied in a card tray with an information label.
70 in stock
Gabbro igneous rock specimens from Balmedie quarry, Aberdeen, Scotland which exhibit a coars grained texture from the crystals. Formed as a mafic pluton intrusion, the samples contain pyroxenes such as augite along side plagioclase feldspar, amphibole and olivine crystals. They are derived from a body known as the Belhelvie basic intrusion which the parent unit being the Caledonian Supersuite. Samples exhibit a grey colouration and density and are suitable for the more serious or professional collector or higher educational use to differentiate similar looking igneous rocks with different compositions and origins. Available in three sizes, the specimens come supplied in a card tray with an information label.
44 in stock
Amygdaloidal basalt, showing instead, gas vesicles (bubbles) with epidote crystals as opposed to the usual quartz and calcites normally expected. Specimens come from the Isle of Skye and are available in various sizes, each rock will come in a card tray with an information label.
Out of stock
This granite pegmatite contains large sheets of muscovite mica, orthoclase feldspar and quartz matrix. An excellent teaching material which comes from Southern Norway. Each specimen comes in a labelled card tray.
Out of stock
Pink granite rock specimens from China, containing the expected granite minerals, however, these specimens are higher in biotite mica, thus making the pieces seem darker than other pink granites.
89 in stock
Phonolite igneous rock specimens, an intrusive crystalline version of nepheline syenite, this rock lies between felsic and mafic composition, collected from Traprain Law, Soctland, the name of the rock is derived from the ancient Greek word which means ‘sounding stone’. Which alludes to the feature this rock has of emitting a metallic ringing when struck. Samples are available in various sizes and come supplied in a card tray with a label.
69 in stock
Micro Granite is a variation of the granite group of rocks, composed of the minerals quartz, feldspar and mica. These particular samples were collected from Threlkeld quarry, Cumbria, UK. They are supplied in a small white tray with an information label.
197 in stock
Grey granite rock specimens from Scotland, featuring the main mineral components expected in granite such as quartz, feldspar and mica. The quartz is slightly smokey, giving the specimens an overall grey appearance. Available in 3 optional size.
Out of stock
Pink Granite, rich in potassium feldspars giving the distinctive pink hue, easily identifiable as a granite due to its mineral composition. Specimens come from Scotland and are supplied in a card tray with label.
8 in stock
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