Aswan Granite in Alexandria
Granite is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. Granites can be predominantly white, pink, or grey in colour, depending on their mineralogy. The word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. By definition, granite is an igneous rock with at least 20% quartz and up to 65% alkali feldspar by volume.
The term "granitic" means granite-like and is applied to granite and a group of intrusive igneous rocks with similar textures and slight variations in composition and origin. These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals, which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter colour minerals. Occasionally some individual crystals (phenocrysts) are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is known as a granite porphyry. Granitoid is a general, descriptive field term for lighter-coloured, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids.
Granite differs from granodiorite in that at least 35% of the feldspar in granite is alkali feldspar as opposed to plagioclase; it is the potassium feldspar that gives many types of granite a distinctive pink colour. The extrusive igneous rock equivalent of granite is rhyolite.
Granite is nearly always massive (lacking any internal structures), hard and tough, and therefore it has gained widespread use throughout human history, and more recently as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm3 (165.4 - 171.7 lb/ft3), its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3–6 • 1019 Pa·s.
The melting temperature of dry granite at ambient pressure is 1215–1260 °C (2219–2300 °F); it is strongly reduced in the presence of water, down to 650 °C at a few kBar pressure.
Granite has poor primary permeability, but strong secondary permeability.
Origin
Granite has a felsic composition and is more common in recent geologic time in contrast to Earth's ultramafic ancient igneous history. Felsic rocks are less dense than mafic and ultramafic rocks, and thus they tend to escape subduction, whereas basaltic or gabbroic rocks tend to sink into the mantle beneath the granitic rocks of the continental cratons. Therefore, granitic rocks form the basement of all land continents.
Aswan Red Granite from Egypt
Description: Aswan Red granite is a coarse to very coarse-grained, uniformly red/black/orange granite of the Precambrian period.
The Precambrian (or Pre-Cambrian) is the earliest period of Earth's history, set before the current Phanerozoic Eon. The Precambrian (coloured green on the right) is a supereon that is subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale. It spans from the formation of Earth about 4.567 billion years ago (Ga) to the beginning of the Cambrian Period, about 541 million years ago (Ma), when hard-shelled creatures first appeared in abundance. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 89% of geologic time.
This stone internationally may be nominated as a granite and in the area of application of the European Standard this stone must be nominated as a granite. During the polishing process a clear epoxy resin filler may be used to fill any micro fissures or tiny pitting however this does not affect the integrity of the stone, it merely provides an even smoother surface finish. Aswan Red Granite is suitable for both interior and exterior use furthermore is frost resistant and with a constant polish.
Aswan Red Granit and his Variations
Aswan Red Granite has a lot of different colour variations.
Variation 1:
Variation 2:
Variation 3:
Variation 4:
Variation 5:
Variation 6:
Log conditions:
At the listing coordinates you have an overview to the place with the magnificent Pompey’s Pillar and to the Red Granite Sphinx. Answer the following question:
1. Look to the column and to the Sphinx. Describe the structure and the various colour of the granite.
2. Look at the listing text and find out which structural variation the column and the sphinx have. Find out if both structures are the same.
3. Describe the visible minerals in the granite, in which way the sunlight is reflected - are certain colours better reflected, if so, which? Why do you think that this effect occurs?
4. Take a picture of the area with your GPS and the column and the Sphinx in the background and insert it within your log.
Send the answers of the questions to Fam.Weiss with your GC-name in the subject-line. We contact you if something is wrong.
Attention – Please note!
Please don´'t write the answers into your internet-log at GC!
Log entries without answering the questions will be deleted by us directly without any further enquiry!
Attention: To fulfill the log condition you have to send a reply mail with the answers for the questions per Geocaching account! A "multiple answer mail" for several Geocaching accounts therefore only fulfills the log condition for the respective sender! The logs of the other accounts are deleted without comment!
