This invention relates to an optical glass of the optical position nd (refraction index) = 1.650 .+-. 2 .times. 10.sup..sup.-3 and vd (Abbe number) = 55.5 .+-. 1.0.
Glasses of this optical position are conventional; however heretofore, all of these glasses had a very low chemical stability. Consequently, there were restrictions on their manufacture and application.