Natural Blue Fire Labradorite Faceted Israel Cut Beads The length of Strand is 14 Inches and Size 3 to 3.5mm approx. Labradorite a feldspar mineral, is an intermediate to calcic member of the plagioclase series. Labradorescence is a side-effect of the molecular change which occurs in large crystal masses of anorthosite, producing an iridescent play of color.