Experimental petrology it is possible to examine the behavior of a magma body as it slowly cools and crystallizes over time Experimental petrology Experimental petrology is the field of research concerned with experimentally determining the physical and chemical behaviour of rocks and their constituents. Because there is no way to directly observe or measure deep earth processes, geochemists rely on experimental petrology to establish quantitative values and relationships in order to construct models of the deep earth. Experimental petrology can range from creating artificial magmas to measure crystallization behavior to observing recrystallization of minerals at varying P/T (Pressure/Temperature) conditions. Although methodology varies
What Is and What Should Never Be descending riff [of "What Is and What Should Never Be"] is amazing: It's like a bow is being drawn back, and then it releases. The rhythm of the vocals is almost like a rap. It's insane — one of their most psychedelic songs." This was also one of the first songs recorded by the band for which Robert Plant received writing credit. According to rock journalist Stephen Davis, the author of the Led Zeppelin biography "Hammer of the Gods: The Led Zeppelin Saga", the lyrics for this song reflect a romance Plant had with his wife's younger sister. "What Is