The backbone of a rockWhen you walk outside and pick up a rock, what are you actually holding? When

The backbone of a rockWhen you walk outside and pick up a rock, what are you actually holding? When you lean against a brick wall, what are you leaning up against?The chemistry answer to this question is “mostly empty space” – most of the volume of every atom is empty space occupied by moving electrons, so from a chemistry perspective that answer is correct and adequate. Geologists, however, tend to look at bigger systems. We consider lots of atoms and how they behave in bulk, so the geologist would probably give a different answer. For a most solids on Earth, it turns out the geologist’s answer is “oxygen”.Oxygen is the backbone of virtually every rock we see at Earth’s surface (with the exception of things like metals or native elements such as coal). It doesn’t matter whether you’re picking up a scoop of dirt or holding a rock; whatever you’ve got is extremely likely to be held together by oxygen.The most common exposure most of us have to oxygen is in the air, where oxygen is neutrally charged and covalently bonded to another oxygen atom (you just took a breath didn’t you?). However, that’s not what oxygen usually does – it takes energy to turn oxygen into a neutrally charged atom. Instead, oxygen really likes having a negative charge and bonding with whatever positively charged atoms it can find.When bonds with atoms as an ion it can build a variety of structures. The most common setup in the earth is a silicate – a silicon ion surrounded by 4 oxygen atoms that make a tetrahedron around it. In this structure, oxygen can serve as a bridge – with single oxygen atoms shared between multiple silicon atoms, allowing the mineral structure to repeat and forming larger crystals.The examples you see here are types of pyroxene structures – the upper mineral in particular is particularly common, making up between 20-40% of the Earth’s upper mantle. The oxygen atoms are the larger spheres that surround the smaller silicon atoms at the center. In that structure, oxygen atoms form long chains and other atoms, like calcium, iron, or magnesium, are stuck in smaller spaces in-between the chains to balance the charges.This is just one possible arrangement of oxygen atoms; the universe gets a little creative with all the varieties. The lower mineral is called wollastonite, it shows up commonly in metamorphic rocks, and you can see that the position of the atoms has changed slightly from one mineral to the next. These minerals are related so there are only small changes in structure, but different mineral groups are formed when the oxygens are fully rearranged. For example, oxygen atoms can be not shared at all, shared with up to 4 different silicon atoms, or anything in-between, and each of those setups creates a different group of minerals. There can aso be no silicon at all like in carbonates, and all sorts of other elements can be stuck in spaces in-between, from heavy as uranium to the lowest-mass element, hydrogen.This one, useful element makes up about ½ of the atoms in Earth’s Mantle. The bonds oxygen makes absorb your weight and keep you from falling downward under the force of gravity. Oxygen: the air we breathe and the backbone of the ground we stand on. Is there anything it can’t do?-JBBImage credit: http://bit.ly/1LXTfoCRead more:https://books.google.com/books?isbn=1429255196http://bit.ly/1oKcSEH -- source link

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