yedrow Posted September 5, 2012 Report Share Posted September 5, 2012 In my pottery studies I read somewhere that clay was a crystalline solid that upon vitrification became amorphic. But, a little while ago I was reading about mineralogy and the article said that clay was by nature amorphic (and of course not a mineral). Then I read an article that referred to it as crystalline. When I thought about it, clay doesn't actually behave 'crystalline'. Does anyone know which it is? Joel. Link to comment Share on other sites More sharing options...
atanzey Posted September 5, 2012 Report Share Posted September 5, 2012 This is from 'An Introduction to Geotechncial Engineering", Chapter 4, Clay Minerals and Soil Structure: Clay minerals are very tiny crystalline substances evolved primarily from Chemical weathering of certain rock-forming materials. Chemically, they are hydrous aluminosilcates plus other metallic ions. All clay minerals are very small colloidal-sized crystals and they can only be seen with an electron microscope. The individual crystals look like tiny plates or flakes, and from X-ray diffraction studies scientists have determined that these flakes consist of many crystal sheets which have a repeating atomic structure. In fact, there are only two fundamental crystal sheets, the tetrahedral or silica, and the octahedral or alumina sheets. The particular way in which these sheets are stacked, together with different bonding and different metallic ions in the crystal lattice, constitute the different clay minerals. It goes on (at length) to discuss the ionic bonding, complete with chemical bonding schematics. Very interesting, if you like that sort of thing. Which, of course, being an engineer I do...... If you like the detail, and have access to an engineering library, it's Holtz and Kovacs -a basic geotechnical textbook. There's probably similar discussion in other geotechnical textbooks. Alice Link to comment Share on other sites More sharing options...
yedrow Posted September 5, 2012 Author Report Share Posted September 5, 2012 Thank's Alice, I needed an engineer's perspective. I did know that clay was made of one sheet of alumina and one silica tetrahedra (or, I think, two alumina octahedra in macaloids). In fact, my son and I were discussing exactly that earlier that day. Then, I read this article on minerology, and I totally forgot that there was a short range organization. Moreover, a mineral cannot be just any type of solid but must be a crystalline one—that is, a solid in which the constituent parts have a simple and definite geometric arrangement that is repeated in all directions. This rule, for instance, eliminates clay, an example of an amorphous solid. http://www.sciencecl...b#ixzz25bZIZgRb What is confusing now it the definition of crystal or crystalline lattice. Is the point of discrepancy here the range of the crystalline organization? Or is the article I read simply wrong? Joel. Link to comment Share on other sites More sharing options...
atanzey Posted September 5, 2012 Report Share Posted September 5, 2012 Joel - I need to look closer at that when I'm not supposed to be working.... But my first thought is that this might possibly have to do with a double crystalline effect going on. The clay particles themselves are crystalline, and the ionic bonds can create a crystalline structure between the particles. That's what you see in a glaze that looks 'solid' and when you shake it, it becomes liquid.... If I have better organized thoughts about this after I can read the article, I'll chime in again! Alice Link to comment Share on other sites More sharing options...
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