html5-img
1 / 21

Crystal Growth

Crystal Growth. GLY 4200 Fall, 2012. 1. Mineral Size. Mineral size - nm’s to tens of meters Mineral mass - nanograms to megagrams Stibnite crystals. Methods of Crystal Growth. From solution, usually aqueous From a melt By sublimation from a gas phase. Nucleation.

denzel
Download Presentation

Crystal Growth

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Crystal Growth GLY 4200 Fall, 2012 1

  2. Mineral Size • Mineral size - nm’s to tens of meters • Mineral mass - nanograms to megagrams • Stibnite crystals

  3. Methods of Crystal Growth • From solution, usually aqueous • From a melt • By sublimation from a gas phase

  4. Nucleation • Usually form from the initial crystallization products of solutions or melts • Various ions must combine to form an initial regular structure pattern of a crystal • Usually requires supersaturation

  5. Supersaturation • Achieved by: • Increasing concentration • Changing temperature • Changing pressure • Rate of change is important • Slow cooling leads to a few nuclei and large crystals • Rapid cooling leads to many nuclei, small crystals

  6. Melts • Growth is similar to aqueous dehydration • High temperatures mean large thermal vibrations, which quickly break atomic clusters apart, destroying nuclei • Low temperatures allow the attractive forces to overcome thermal vibration holding clusters together

  7. Growth From Melt

  8. Vapor • Cooling allows dissociated atoms or molecules to join • Examples: • Formation of snowflakes • Growth of ice on a window • Formation of sulfur crystals around fumaroles

  9. Destruction of Nuclei • Nuclei have very large surface area/volume • Unsatisfied bonding on outer surfaces leads to dissolution • Crystallization only takes place when some nuclei survive long enough for growth to occur

  10. Critical Size • If nuclei grow rapidly, their surface area/volume declines, and they may reach and exceed a critical size • Above the critical size, the nuclei are relatively stable, and growth can begin

  11. Law of Bravais • The most likely crystal face to grow are those planes having the highest density of lattice points • However, these faces have lowest surface energy • This makes them stable, but slow growing • Anions or cations in solution are not attracted to these faces

  12. Rate of Growth • Faces composed of all anions or all cations are very high energy • They attract ions of the opposite sign, and grow rapidly • Eventually they grow themselves out of existence, leaving the slower growing faces

  13. Vectorial Properties • Some properties of crystals depend on the direction in which they are measured • These are called vectorial properties • Examples: Hardness, electrical and thermal conductivity, speed of light, speed of seismic waves, thermal expansion, solution rate, and diffraction of X-rays

  14. Variation of Vectorial Properties • Many vectorial properties vary discontinuously as direction is changed • Values of these properties pertain to a given crystallographic direction • Values of the property in crystallographic directions intermediate to two given directions do not very smoothly as the direction is changed

  15. Discontinuous Vectorial Properties Examples • Color banding in minerals • Dendritic growth • Rate of solution etching by a solvent • Cleavage • Hardness

  16. Color Bands • Tourmaline often shows color banding

  17. Dendritic Mineral Habit • Dendritic formation of bright native silver crystals. • State of Maine Mine, Tombstone District, Cochise Co., Arizona, USA

  18. Continuous Vectorial Properties Examples • Index of refraction, related to the velocity of light • Seismic velocities in crystals • Electrical and thermal conductivity • Thermal expansivity

  19. Crystal Intergrowths • During crystal growth, one crystalline substance may grow on a crystalline substance of different composition and structure • Such growths are known as epitaxial growths

  20. Epitaxial Overgrowth Examples • The (010) plane of staurolite has a structure similar to kyanite • Kyanite’s (100) may epitaxially overgrow staurolite • Similarly, plagioclase sometimes overgrows microcline.

  21. Epitaxis Photo • Epitaxial overgrowth of quartz on epidote • Green Monster Mine,Prince of Wales Island,Alaska

More Related