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The rock that we are presenting to you looks as if it had been decorated with blue inkblots. It was presented to us as "azurite granite". It is reported that it is found at the foot of the K2 mountain in northern Pakistan. Therefore it is also offered under the trade name "K2".
The structures we saw in our microscopic investigation was similar to that of gneiss. Quartz, biotite and feldspar crystals and a weakly pronounced, layered structure were easily recognizable. In addition, small grains of a green mineral and these strange blue spots are readily visible with the naked eye.
The carbonate test with 10% diluted hydrochloric acid showed an unspecific reaction pattern. The green mineral reacted promptly to the acid, classifying it as malachite. In the rest of the rock a weak but irregular reaction could be observed, no matter whether these domains were green, blue or colorless. It seemed as if carbonatic minerals had penetrated the whole stone.
The occurrence of basic copper carbonates such as azurite and malachite (which are typical for sedimentary deposits) in a metamorphic gneiss is highly unusual. Therefore, we decided to clarify the mineral composition by means of X-ray diffraction analysis (EDX).
In modern mineralogy, "bronzite" is no longer regarded as a mineral in its own right, but as an iron-bearing variety of the mineral enstatite (so-called "Ferro-Enstatite", abbreviated: "Fe-Enstatite", (Mg,Fe)2[Si2O6],). Fe-Enstatite of the variety Bronzite contains 5 - 15% iron (in relation to magnesium) and belongs to the mineral group of pyroxenes. This group comprises single chain silicates with the basic component [Si2O6].
In most cases Fe-Enstatite is a rather unimpressive mineral. In its earthy, brownish to almost black colors it is neither rare nor valuable. But as soon as it appears as shiny golden flakes and bars, it attracts the interest of mineral dealers and collectors.
The golden-yellow shining "bronzite", which is available as tumbled stones, does not consist solely of the mineral Ferro-Enstatite, but also of other minerals. It is a rock in which Fe-Enstatite is the main component in company with black magnetite and colorless quartz. For this reason, the hardness of this rock varies between 5 to 6 (bronzite) and 7 (quartz). The density of the rock is about 3.2 - 3.4.
