Pyroclastic rocks are the product of explosive volcanism. They are often felsic (high in silica). Pyroclastic rocks are often the result of volcanic debris, such as ash, bombs and tephra, and other volcanic ejecta.henocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye. Rhomb porphyry is an example with large rhomb shaped phenocrysts embedded in a very fine grained matrix. Volcanic rocks often have a vesicular texture caused by voids left by volatiles trapped in the molten lava.
July 9, 2014. Frozen sperm must be stored in extremely cold temperatures (-196 F), but in order to ensure that the fewest possible sperm are damaged, the freezing must be gradual. Generally, the following procedure is followed:
In man, about 50% of spermatozoa are stored in the cauda (tail) of the epididymis, with the average time of storage in the epididymis between 10 and 20 days. Sperm can be damaged during epididymal storage by elevated temperature (such as in the presence of a varicocele), infection, or other hostile conditions.