Sentence:  There is a general error prevalent that mica is <WSD>isinglass</WSD>, and many times it is spoken of as <WSD>isinglass</WSD>, but there is a great difference between the two. Mica is mainly composed of silicate of aluminum, while <WSD>isinglass</WSD> is a fish gelatine or glue ... 
Meaning of the word marked with <WSD> tags:  A thin, transparent sheet of mica (probably from its similarity to true isinglass).