Plagioclase is a group of
Like many other such
groups, it is a series of solid solutions between the sodium end
albite, and the calcium end anorthite.
Between the two are
oligoclase, andesine, labradorite and bytownite.
Most are colourless,
white, grey, brown or green, but labradorite is blue.
By Miguel Vera León via Flickr.com
In thin sections they
typically look like on the photo above.