Dec 01, 1997  Summary. Earthquake prediction research has been conducted for over 100 years with no obvious successes. Claims of breakthroughs have failed to withstand scrut.

Unusual Snow Crystals Natural Snowflakes        --Unusual Forms             Designer Snowflakes                   Snowflake Physics                  Snow Activities           Snowflake Touring         Unusual Snow Crystals. Some exotic examples from the snow crystal menagerie. In addition to the normal snowflake forms (see ), there are also many unusual shapes that can be found floating from the sky.  Some of these are described here, with photos from the Rasmussen&Libbrecht collection (see ). And, of course, you can find even more in our.

Not Your Ordinary Snow. 12-Sided Snowflakes   A bit of snowflake watching may turn up some 12-sided snowflakes, as these occur along with the normal 6-sided variety. They're not real common, but you can spot them if you look.  Some snowfalls bring quite a few twelve-siders, although no one really knows what weather conditions are best for making them. Triangular Snowflakes   You won't find any 4-, 5-, or 8-sided snowflakes in the wild, but you may spy some 3-sided crystals.  As with the 12-siders, these crystals appear along with the more common hexagonal variety.  And again, their origin is still something of a mystery. Bullets    Bullets form when several columnar crystals grow from a single nucleus, a beginning that is similar to the spatial dendrites (see ).

Bullets always start out in clusters, but the clusters can break up to yield individual bullet crystals. Arrowhead Crystals     Crystal twinning is a phenomenon whereby two crystals grow out of a single seed and have a specific crystallographic orientation relative to one another. One example is found in arrowhead crystals, which occur along with columns.  The unusual shape results from the way the two crystal halves are joined. The seam between the crystals can be seen when some of the ice evaporates, leaving an evaporation groove, as indicated in the picture at right.  Twin Prisms    Another example of crystal twinning occurs when twin columns grow from a common center, one rotated 60 degrees relative to the other.  The growth looks like an ordinary column, but again we can find an evaporation groove that indicates twinning. Twelve-sided snowflakes also form by columnar twinning; in this case the two columns are rotated 30 degrees and the assembly grows into a capped column (see ). Pyramidal Crystals    At very low temperatures one can find snow crystals with pyramidal facets in addition to the usual basal and prism facets (see the ) (photo from Tape [1]).  Sometimes seen at the South Pole, these crystals are exceedingly rare in more benign climates.

Tape, Atmospheric Halos, Antarctic Research Series, Vol. 64, (American Geophysical Union, 1994). Return to SnowCrystals.com was created by, Caltech Comments?  Send an.

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