A variety of feldspar valued as a gem for its pearly translucence.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "moonstone" in a sentence
"The moonstone is another example of this peculiar feature which is possessed in a more or less degree by all the stones in the class of pellucid jewels, but no stone or gem can in any way even rival the curious mixture of opaqueness, translucency, silkiness, milkiness, fire, and the steadfast changeable and prismatic brilliance of colour of the precious opal."
"He took the one I would rather have him take -- a beautiful pearl, like my friendship is for him, shadowed by the moonstone, which is my unworthiness."
"Next is moonstone, which is the creamy off-white one, and finally white quartz, a cloudy pure white stone (and also my favourite of the new bunch)."