Available online
Description
Programme examines: 1 : crystal nucleation and growth from melts. 2; relationship between crystal structure and crystal growth and cleavage planes. 3; use of mineral cleavage traces to identify minerals.
Programme examines: 1 : crystal nucleation and growth from melts. 2; relationship between crystal structure and crystal growth and cleavage planes. 3; use of mineral cleavage traces to identify minerals.
| Item code: | S23-; 02 |
|---|---|
| First transmission date: | 05-02-1972 |
| Published: | 1972 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:21:31 |
| + Show more... | |
| Producer: | Jim Stevenson |
| Contributors: | Ian Gass; Chris Wilson |
| Publisher: | BBC Open University |
| Keyword(s): | Ball bearings; Ball model; Basalt; Crystalline aggregates; Diamond; Gabbro; Graph; NaCl; Porphyritic texture; Volcano |
| Footage description: | Wilson introduces the programme and has a large crystal with him. Ian Gas, with specimen of fine and coarse grained crystalline aggregates. He contrasts the two. Both specimen were made artificially of the same material, but the melt of one cooled much faster than the other. Gass uses a graph to review the process of cooling and crystallization of a melt. (Graph plots degree of supercooling against numbers of nuclei.) Gass with two igneous rock specimen having the same mineral composition but very different grain size. He shows the fine grained basalt in both hand specimen and thin section. He then shows the coarser grained gabbro in the same way. Gass with a sinplified cross section diagram of a volcano. He uses this to place the formation of the above specimen in their natural context. Film shots of active volcano showing lava flow. Gass continues, he goes on to explain the origin of porphyritic texture with reference to the volcanic model. Chris Wilson, with a crystal specimen, briefly points out that mutual interference during crystal growth prevents the development of well shaped crystals. Charles Newey demonstrates that crystals of NaCl can be either thrown as cubes or cleaved into cubes, Newey examines tho structure of NaCl with theaid of a molecular model (a ball model). He uses another model (ball bearing ) to show why NaCl only cleaves along particular planes. He goes on to explain that cleavage is an invariant characteristic of crystals. Crystals of a given substance will always cleave in the same way while crystal growth planes are not necessarily invariant. Newey illustrates some of the different shapes that can be developed by basically cubic sructures such as NaCl. He shows specimen of pyrite, garnet and diamond. Ian Gass returns to show how the invariant pattern of cleavage planes can be used to identify minerals in rocks. Shots of a thin section of gabbro containing pyroxene crystals. Gass uses a model of a pyroxene crystal to demonstrate how the crystal was cut in the thin section. He compares this with another thin section of pyroxene in which two mutually sub-perpendicular sets of cleavage traces are seen. Gass shows a thin section micrograph of an amphibole with cleavage intersections at about 60 degrees. He sums up the programme. Shots of rotating crystals with credits over. |
| Master spool number: | 6LT/70375 |
| Production number: | 00521_2151 |
| Videofinder number: | 1709 |
| Available to public: | no |
