Perthite is either microcline or orthoclase with thin lamellae of exsolved albite. Alkali feldspar dominates, commonly represented by orthoclase and the exsolved lamellar albite, form perthite. In the alkali feldspar almost pure albite domains are observed. Solid solutions between K-feldspar and albite are called "alkali feldspar". Solid solutions between albite and anorthite are called "plagioclase", or more properly "plagioclase feldspar". The plagioclase is sodium-rich, usually albite or oligoclase. There are several named plagioclase feldspars that fall between albite and anorthite in the series. The mineral occurs in pegmatite deposits and is easily mistaken for albite and other feldspars. It occurs in the quartz, albite, sericite, chlorite, garnet assemblage of pelitic schist. The minerals found are quartz, mica, chlorite, albite, sphene, and graphite. The Ragua Unit consists of albite and graphite containing mica schist, and quartzite. Associated minerals are quartz, elbaite, albite and micas. Associated minerals include&colon; quartz, albite, petalite, eucryptite, lepidolite and beryl. Frequently associated minerals include&colon; natrolite, neptunite, joaquinite, serpentine and albite. It is the reflections from these albite laminae that produces the flash.