13 Riveting Rocks

by Deb on May 19, 2011

  1. There is a cave in Mexico called, appropriately, the cave of crystals, where there are gypsum crystals 11m long. They’ve grown because of the combination of heat, humidity and minerals and the extremely stable environment. The cave was filled with mineral rich water at over 50 degrees for half a million years. Cave of Crystals
  2. Geodes are beautiful crystal formations inside bubbles in rocks. The outer rock forms with a bubble, then mineral rich water filters through and layers or crystals form inside. Geode
  3. Tektites are small rocks of natural glass. The most common theory is that they are from meteorite impacts, the rock that meteorites hit is pulverised under extreme heat and pressure and blown into the atmosphere, then solidifies as glass as it drops back to earth. Tektite
  4. And talking about extreme heat and pressure, diamonds are only formed deep inside the earth’s mantle. They are a form of carbon crystals that grow 140-190km down under thick, ancient and stable parts of the crust. They are brought to the surface through volcanic pipes, a type of extremely deep and rare volcano. The diamonds that are mined today are very ancient – at least a billion years old. Rough_diamond
  5. Opals are a  form of silica with tightly packed microscopic spheres. The way these spheres bend and block light gives opal its colours. Opals form when silicon rich water filters through rocks, they can also form fossils as they replace the organic materials. fossil opal
  6. Banded iron are ancienct iron formations that were very important historically because they are relatively easy to mine and smelt. They are a fascinating look at th chemical and biological development of earth. In the early earth the acidic oceans contained lots of dissolved iron. When early life began producing free oxygen it reacted with the iron and deposited a layer of iron oxides. When the oxygen decreased muds that became shales were deposited. There was a cycle of layers as oxygen increased and decreased, it’s not certain what caused it. Eventually the oceans were permanently oxygenated and all the iron was turned into oxides. Banded iron
  7. Conglomerate is an interesting rock because it contains other rocks! It’s a record of ancient water courses that rounded stones and carried them down to lakes or oceans. The sediment carried with them gradually turned to stone around them, forming a new stone with a sandstone matrix around even older rocks. Conglomerate
  8. Mica is another silicate crystal, but they aren’t your typical crystal. They come is flat sheets that can be literally peeled apart. They have been used in windows and still have a huge range of uses today, from electronics and making ultraflat sheets for electron microscopy to the pearlescent glitter in car paint and makeup. Mica windows
  9. Marble is a metamorphic rock, which means it was originally limestone that has been under great heat and pressure which causes the grains to recrystallise and layers to be lost. It can contain fossils. Marble
  10. It’s not known exactly how flint forms, it is found as lumps or nodules of silica inside sedimentary rocks. They were extremely important in ancient times in Europe and Africa because they are extremely fine grained and fracture like glass, so they were used for many stone tools. Later they were important because they make sparks and could be used to start fires, and even later those sparks were used to fire flintlock guns. Flint axe
  11. Obsidian is natural volcanic glass. Glass is silicon dioxide, the same as many types of sand. When it is heated it fuses into an amorphous solid, which can happen in volcanoes as well as furnaces. However obsidian is black. Obsidian
  12. Pele’s Tears are droplets of volcanic glass that were shot into the air and solidified, turning into teardrops. There are other related forms such as Pele’s Hair and limu o Pele, all named after the Hawaiian fire goddess Pele. Pele's Tears
  13. Chalk is Calcium carbonate, the same chemical used by many animals to produce shells and eggs. It forms at the bottom of oceans, where microscopic plankton called diatoms and other shellfish die and settle into vast layers. It is then covered and compressed to form chalk deposits. White cliffs of Dover


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{ 1 comment… read it below or add one }

Brenda May 19, 2011 at 8:51 pm

What beautiful stones. Thanks for sharing.
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