Eight years later, the martian mini-rover Sojourner, in its first analysis of the composition of a martian rock, apparently recorded just the expected composition. Their chemistry and mineralogy are closely similar to those of the diorites. Porphyritic varieties are fairly common, both feromagnesian minerals and feldspars occurring as phenocrysts - the latter commonly showing zoning. Hypersthene and enstatite are more common in andesites than in diorites. Pure glassy andesites are rare, but glass is of frequent occurrence in the groundmass of andesites, commonly in a devitrified state.
Andesites occur as extensive lava flows always associated with continental masses.
The 'Andesite Line' is the boundary between the 'continental' andesitic association and the 'oceanic' basaltic association.