Felsic is a term used in geology to refer to silicate minerals, magmas, and rocks which are enriched in the lighter elements, such as silica, oxygen, aluminium, sodium, and potassium. The term combines the words "feldspar" and "silica."
Felsic minerals are usually light in color and have specific gravities less than 3. Common felsic minerals include quartz, biotite, muscovite, hornblende, orthoclase, and the sodium rich plagioclase feldspars. The most common felsic rock is granite.
On the opposite side of rock spectrum are the iron and magnesium rich "mafic" rocks.
Acid rock, such as granite, is igneous rock with over 60% by weight of silicon dioxide. The term is no longer current as it is incorrectly based on the idea that silicic acid is the chief form of silicon in rocks.
Felsite is a petrologic field term used to refer to very fine grained light colored volcanic rocks that may be later reclassified after more detailed microscopic or chemical analysis.
See also: List of minerals and List of rocks