BBC Jersey - Nature - Times, Tides and Towers (#)
„Cracks in these rocks allowed others, such as the much finer grained aplite and pegamtite to intrude, an effect much in evidence at La Rocque. Much of the granite in the La Rocque area is of the coarse veriety contaning crystals of quartz which gives it a sparking appearance. The larger the mineral crystals in the rocks, the slower they cooled beneath the earth's surface.“
http://www.bbc.co.uk/jersey/therock/nature/ 09.shtml - Cached
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