Sentence:  &#91;[https://books.google.com/books?id=b2gMAQAAIAAJ&pg=PA244 pages 244–245]&#93; <WSD>Aventurine</WSD> is a brown glass flux, containing very small glittering particles, which give it a peculiarly glittering appearance. It was formerly manufactured into objects of art and ornament at Murano near Venice. [...] The statements which are found respecting it in technological works, according to which it is obtained by fusing down with glass minute particles of gold, copper, brass, mica, or talc, are not correct, as the microscopic examination of <WSD>aventurine</WSD> plainly shows. &#91;[https://books.google.com/books?id=b2gMAQAAIAAJ&pg=PA246 page 246]&#93; There can be no doubt therefore that the crystals in the <WSD>aventurine</WSD> consist of metallic copper, which were separated in a crystalline state from the fused glass containing oxide of copper by the addition of some reducing substance. 
Meaning of the word marked with <WSD> tags:  A kind of brownish glass containing gold-coloured spangles.