Granodiorite

Granodiorite is a closely related to the granite igneous rock, which is spread throughout the world and among the plutonic rocks of the earth's crust has a share of 34 percent. It occurs on all continents.

History

The term granodiorite was towards the end of the nineteenth century for the first time by GF Becker used on maps of the Gold Belt in the Sierra Nevada. The first description of the rock comes from W. Lindgren from the year 1893.

Rock description

It is a mostly coarse and medium grained, bulky rock from white gray to gray color. Porphyry -like trained granodiorites with ungleichkörnigem structure can achieve particle sizes of several centimeters in the feldspars. The mineral grains appear directionless arranged, upon closer examination, however, often can be an igneous Einregelungsgefüge at the feldspars recognize. Also the structure of tectonic origin are not uncommon.

Mineral content and composition

Granodiorite contains as granite feldspar, quartz and mica, and is therefore different from the granites hardly. In contrast to the granite granodiorite contains significantly more plagioclase than potassium feldspar, the Plagioklasanteil is at the feldspars between 65 and 90 percent by volume, the modal content of quartz varies between 20 and 60 percent by volume. The content of mafic minerals is usually higher than the granite. They usually consist of hornblende and biotite and give the granodiorite therefore a slightly darker color. With its higher iron and magnesium contents of the granodiorite forms the connecting link between the granite and the diorite ( tonalite ), hence the name of the rock.

Accessory minerals are mostly allanite, apatite, titanite and zircon, and occasionally epidote and zoisite. As opaque ore minerals act ilmenite and magnetite.

Have granodiorites less than 5 percent dark minerals, mainly biotite and hornblende, they are called Leukogranodiorite and over 25 percent Mela - granodiorites.

Modal mineral constituents

Granodiorites have the following modal mineral component ( in volume percent):

• Quartz - 19 to 26 %
• Alkali feldspar - 17 to 21 %
• Plagioclase - 44 to 48 %

• Biotite - 3 to 10%
• Hornblende - 0-7 %
• Clinopyroxene - may be present in rare cases

Accessory minerals and ore minerals can be up to 1.5%.

Chemical composition

Chemically, granodiorites to dacites equivalent, therefore, in the TAS diagram they fall into the field O 3 - SiO 2 -rich granodiorites can also change over the field R of the rhyolites. The average continental crust, the composition of granodiorite. Granodiorite also belongs to the tonalite - granodiorite Trondhjemit series ( TTG ).

Granodiorites are supersaturated SiO2 rocks and corundum - or diopside - normative, their content of these minerals thus corresponds to the normative mineral composition. Your SiO2 content varies usually 63-68 percent by weight, but also may be substantially higher (up to 73 weight percent). The weight fraction of Na2O and K2O varies 6-8 percent. On the basis of their K2O content, they belong to the middle, but in most cases already for the high -K type (they are thus kalkalkalisch ). Your magnesium number Mg # moves by 0.52. Your Aluminosität (A ' / F ratio, A' = Al2O3, Fe2O3 - Na2O - K2O - CaO, FeO MnO F = MgO) is usually normal, although the Half Dome granodiorite eg hypaluminos (A '/ F <0). Some varieties can be peraluminos (A ' / F> 0.33). The ratio of aluminum to the sum of the alkalis and calcium (Al / K Na Ca ) is less than 1.1, therefore granodiorites belong mainly to the I- type intrusive, but even here there are exceptions ( metasedimentärer S- type > 1, 1).

The following table shows the chemical composition and CIPW norm of an average granodiorite (average of 885 analyzes), further analyzes of the Half Dome granodiorite (SiO2 - poor ) and the Cathedral Peak granodiorite - (SiO2 - rich ). The trace elements are from the Cathedral Peak granodiorite and from Deddick granodiorite at Mount Kosciuszko in southeastern Australia:

Varieties and types

From granodiorite following varieties are known:

• Biotite granodiorite
• Hornblende granodiorite
• Hornblende - biotite granodiorite

Can also be distinguished in granodiorites between I- and S- type Tpyus As with the granite, where S - types have more than 1 percent normative corundum.

Crystallization

The presence of biotite and hornblende in particular indicated a water content of 3 to 5 percent for granodioritic magmas. Crystallization experiments confirm the dominant position of plagioclase during crystallization history, which crystallizes together with biotite, hornblende, and accessory minerals ore minerals over a wide temperature range. Shortly before reaching the solidus then crystallize also quartz and alkali, usually as a gusset filler between the relatively tall, usually isomorphic plagioclase.

Inclusions

Granodiorites may occasionally contain inclusions or enclaves of mafic rocks foreign, mostly SiO2 - poor rocks such as diorite, quartz diorite or gabbro. It sometimes can also be Xenokristalle and the so-called enclaves surmicacées, biotite inclusions. Conversely, granodiorites can be included in a foreign rocks.

Occurrence

The presence of granodiorite worldwide. As the equivalent dacites they are mainly linked to subduction zones active continental margins.

Larger Granodioritvorkommen find consequently in the Sierra Nevada in the western North America and the Peruvian Küstenbatholit.

Numerous granodiorites originated in the Paleozoic in the Lachlan Fold Belt in Australia.

In Europe it is found in Finland, France ( Massif Central and the Pyrenees ), Italy ( Adamello, Elba, Giglio, Presanella, Rieserfernergruppe, Tuscany ), Slovakia and Czech Republic. In Germany it is mainly in the Bavarian Forest, the Erzgebirge, Fichtelgebirge, resin, Lusatian Mountains, the Odenwald and the Black Forest to be found in Austria in Freistadt in Upper Austria.

Physical Properties

Granodiorite is a relatively light rock, its density moves from 2.64 to 2.70 g/cm3.

Thin section images

Granodiorite with crossed polarizers

Granodiorite from Slovakia, crossed polarizers

Use

Granodiorites have similar technical characteristics as the Granite. They can be processed on all types and taken to polishing.

Granodiorites are processed since ancient times. In Roman times granodiorite was a sought-after raw material and has been mined for example in Mons Claudianus in Egypt. Because of their resistance to granodiorites are well suited for floor and stair coverings, wall coverings of facades and as grit for road paving.

Colloquially, the term granodiorite has hardly been used since the difference between granite and granodiorite is generally not known. Therefore granodiorites are referred to as granite natural stone trade and arrive in the trade.

Types of natural stone

• Lusatian granodiorite ( Demitz - Thumitz and numerous other places, Saxony ) is incidentally acted as Lusatian granite.
• Tittlinger granodiorite ( Tittling ), Bavaria
• Special Bacher granodiorite ( Sonderbach ), Hesse
• Skutečská granodiorite ( at Ctětín, Okres Chrudim, Bohemia) is commonly referred to as Skutečská granite.

• Stone pattern of granodiorites

Granodiorite from the deposit of Švihov (Czech Republic)

Granodiorite from the deposit of Ctětín (Czech Republic)