So the internal structure of quartz is not as tight as it first seemed. Since this is a top view of a three-dimensional crystal, these gaps are actually channels that run through the entire crystal, parallel to the c-axis. There are apparently hexagonal patterns that correspond to the six-sided prism of the crystal, a few examples are shown in Fig.2.03.Īnother interesting feature are black holes, gaps in the structure. If we change the perspective to a top view of the crystal (looking down the c-axis, Fig.2.02), the relationship between the arrangement of atoms and the external shape becomes more obvious. The first impression is that of a very densely packed structure.įig.2.02: Top view of the quartz crystal model But to explain the internal structure and the symmetry properties, it is good enough.Īs one would expect from a crystal, one can see that there are some repeating patterns, so there is a regular structure, but as a whole it looks quite complex. Also note that while the relative positions of the atoms are correct, this is probably not an accurate model of quartz surface structure (I do not have any empirical data on that). Of course, this rendering is based on the assumption that atoms are just small, hard balls of identical size. In an ordinary microscope this crystal would be invisible. This crystal would be about 7 nanometers high - 143,000 of such crystals would line up to one millimeter. The first picture (Fig.2.01) is a computer rendering of what a tiny quartz crystal might look like in a fantasy microscope that could resolve individual atoms. Introduction - Looking through a Microscopeįig.2.01: Idealized model of a quartz crystal This corresponds to a projection of the atoms onto the a-plane and the c-plane, and not to a slice of the crystal: the atoms one sees actually lie in different planes along the a- and the c-axis. To get an idea of quartz crystal structure and its symmetry properties, most figures show the crystal when viewed in the direction of either the a-axis or the c-axis ( a and c in Fig.1.01). This chapter introduces the crystal structure of quartz and its relation to the symmetry and the physical properties of quartz crystals.Īll renderings are based on a single data set of quartz unit cell coordinates downloaded from the now orphaned site Fig.1.01: Projection of quartz crystal structure onto a- and c-planes The very largest, meanwhile, are up to 36 feet (11 meters) long and 3.2 feet (1 meter) thick.Document status: usable, section on twinning missing Many are 13.1 to 19.6 feet ( 4 to 6 meters) in length. Nevertheless, over time, a lot of these things attained breathtaking sizes. A 2011 study argued that, under the conditions that were available in this cave, it would've taken anywhere from 500,000 to 900,000 years to grow a selenite crystal measuring 3.2 feet (1 meter) in diameter. Granted, the crystals didn't turn into giants overnight. Because the crystals remained underwater - and because the water temperature stayed within a few degrees of 136 degrees Fahrenheit (58 degrees Celsius) - they were able to keep growing continuously. White-tinted selenite crystals took over the cave. The particles slowly began recombining into a kind of gypsum known as selenite. After that happened, the anhydrate started breaking down, filling the water with calcium and sulfate. Eventually, however, the H2O's temperature dipped slightly below 136 degrees Fahrenheit (58 degrees Celsius). The magma underneath Giant Crystal Cave kept the water in the cave nice and hot. (That's a reversible transformation, by the way.) But at lower temperatures, the mineral is liable to dissolve and then reform as gypsum. Now at temperatures of 136 degrees Fahrenheit ( 58 degrees Celsius) or more, anhydrite remains stable.
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