Sedimentary, Igneous, Metamorphic :: Part TWO

[Rough Draft 1st]

DIOROTE of Puma Punku
Article in Progress by Pat Darnell and Saul Buck

It was known since antiquity for its hardness and was used for building by the Maya and the Inca in foundations, and by Islamic architects too, as material for pavements. Due to its hardness, it was used to create intricate artifacts. The Egyptians used it to fashion granite due to its very hardness.
It is extremely rare to come by and is found in the Andes mountains, Sondrio in Italy, Thuringia and Sassonia in Germany, Scotland, the Isle of Guernsey, Minnesota USA, Sweden and Romania.

Cuzco was an Inca stonghold until the invasion of the Spanish colonials who then trashed the place. There are still quite a few buildings built on Inca foundations. Truly amazing how they jig-sawed all the huge diorite blocks together with no mortar. And diorite is an igneous rock that is very hard indeed. You can see it here www.unique-southamerica-travel-experience.com/images/inca-stonework-copia.jpg
Equally interesting is how the Inca empire was only 100 years old when it sucumbed to Pizarro and his boys. Short and sweet. (SOURCE)

Quality of the stonework, and immense size of the stones makes this ruin very puzzling. Details in the stonework are hardly possible achievable tolerances in today's stone carving.

Personally, this is the first time I have looked at a surface that comes to us from out of antiquity and said to myself: That is not possible. Stone specifications for wall construction have a "flatness factor" that must be kept a small number. These stone slabs are as flat as if this was polished with a twenty step coarseness grinder\sander. I am truly baffled.

Dolomite might have been agood stone to work with in ancient times, but guess what? These stones are igneous formed Diorite, a kind of granite or gabbro...

Granite is a coarse-grained rock found in plutons—large, deep-seated bodies of rock that slowly cooled from the molten state. Thus it is the typical plutonic rock. Granite is thought to form as hot fluids from deeper in the mantle rise and trigger widespread melting in the continental crust. This gallery shows some of the variety of granites.
Diorite is a plutonic rock that is something between a granite and a gabbro. It consists mostly of white plagioclase feldspar and black hornblende.

Hardness: Hardness (as measured with the Mohs scale) actually refers to minerals rather than rocks, so a rock may be crumbly yet consist of hard minerals. But in simple terms, "hard" rock scratches glass and steel, usually signifying the minerals quartz or feldspar (Mohs hardness 6-7 and up); "soft" rock does not scratch a steel knife but scratches fingernails (Mohs 3-5.5); "very soft" rock does not scratch fingernails (Mohs 1-2). Igneous rocks are always hard.

Part Two: Why is the difference between Dolomite and Diorite?

The Granitoid Criterion
A granitoid meets two criteria: (1) it is a plutonic rock that (2) has between 20 percent and 60 percent quartz.

Chemical composition
A worldwide average of the average proportion of the different chemical components in granites, in descending order by weight percent, is:
•SiO2Silicon dioxide
The chemical compound 'silicon dioxide', also known as 'silica' , is an oxide of silicon with a chemical formula of and has been known for its hardness since antiquity....
— 72.04%
•Al2O3Aluminium oxide
Aluminium oxide is an amphoteric oxide of aluminium with the chemical formula 23. It is also commonly referred to as alumina or aloxite in the mining, ceramic and materials science communities....
— 14.42%
•K2OPotassium oxide
Potassium oxide is a Chemical compound of potassium and oxygen. This pale yellow solid, the simplest oxide of potassium, is a rarely encountered, highly reactive species....
— 4.12%
•Na2OSodium oxide
Sodium oxide is a chemical compound with the formula Sodium2Oxygen. It is used in ceramics and glasses. Treatment with water affords sodium hydroxide....
— 3.69%
•CaOCalcium oxide
Calcium oxide , commonly known as burnt lime, Lime or quicklime, is a widely used chemical compound. It is a white, Caustic and alkaline crystalline solid at room temperature....
— 1.82%
•FeOIron(II) oxide
Iron oxide, also known as ferrous oxide, iron oxide/oxidized iron or more commonly rusted iron, is one of the iron oxides. It is a black-colored powder with the chemical formula ....
— 1.68%
•Fe2O3Iron(III) oxide
Iron oxide?also known as ferric oxide, Hematite, red iron oxide, synthetic maghemite, colcothar, or simply rust?is one of the several oxide Chemical compounds of iron, and has Paramagnetism properties....
— 1.22%
•MgOMagnesium oxide
Magnesium oxide, or magnesia, is a white solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of ....
— 0.71%
•TiO2Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula titaniumoxygen2....
— 0.30%
•P2O5Phosphorus pentoxide
Phosphorus pentoxide is a chemical compound with formula Phosphorus2Oxygen5. This white crystalline solid is the anhydride of phosphoric acid....
— 0.12%
•MnOManganese(II) oxide
Manganese oxide is the chemical compound with formula MnO. It occurs in nature as the rare mineral manganosite.Preparation and chemistry...
— 0.05%
Based on 2485 analyses

Plagioclase tends to be more transparent than alkali feldspar; it also very commonly shows striations on its cleavage faces that are caused by multiple crystal twinning within grains. These appear as the lines in this polished specimen.

One way is to determine the mineral's density by putting crushed grains in immersion oils of different densities. (Albite's specific gravity is 2.62, anorthite's is 2.74, and the others fall in between.) The really precise way is to use thin sections under the petrographic microscope, determining the optical properties along the different crystallographic axes.

The amateur has a harder time. Large grains of plagioclase like this specimen display two good cleavages that are off square at 94° (plagioclase means "slanted breakage" in scientific Latin). The play of light in these large grains is also distinctive, resulting from optical interference inside the mineral.

The igneous rocks basalt (extrusive) and gabbro (intrusive) contain feldspar that is almost exclusively plagioclase. True granite contains both alkali and plagioclase feldspars. A rock consisting of only plagioclase is called anorthosite.

A noteworthy occurrence of this unusual rock type makes up the heart of New York's Adirondack Mountains (see the next page of this gallery); another one is the Moon. This specimen, a gravestone, is an example of anorthosite with less than 10 percent dark minerals.

Granite has been intruded into the crustCrust (geology)

In geology, a crust is the outermost solid shell of a planet or moon, which is chemically distinct from the underlying mantle . Crusts of Earth , our Moon, Mercury , Venus, and Mars have been generated largely by igneous processes, and these crusts are richer in incompatible elements than their respective mantle s....
of the EarthEarth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
during all geologic periods, although much of it is of PrecambrianPrecambrian
The Precambrian is an informal name for the supereon comprising the eon of the geologic timescale that came before the current Phanerozoic eon....
age. Granitic rock is widely distributed throughout the continental crustContinental crust

The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as Continental shelf....
of the Earth and is the most abundant basement rockBasement rock
Basement rock usually refers to the thick foundation of ancient, and oldest metamorphic and igneous rock that forms the Crust of continents, often in the form of granite....
that underlies the relatively thin sedimentarySedimentary rock
Sedimentary rock is one of the three main Rock types . Sedimentary rock is formed by deposition and consolidation of mineral and organic material and from precipitation of minerals from solution....
veneer of the continents.

Despite being fairly common throughout the world, certain areas are well known for their commercial granite quarries:

•Brazil, South America -- officially the Federative Republic of Brazil , is a country in South America. It is the List of countries and outlying territories by total area country by geographical area, occupying nearly half of South America, the List of countries by population country, and the fourth most populous democracy in the world.... [SOURCE]
http://www.absoluteastronomy.com/topics/Granite 
[Article to be proofed and drawn corrected at later date]

Next Week: Popular MAR's -- Sedimentary, Igneous, Metamorphic