Apparently, when Jessica elopes with Lorenzo, she not only helps herself to a ton of Shylock's gold, but she also steals a turquoise ring, which turns out to be one of Shylock's most prized possessions.
When Solanio describes Shylock's reaction to Jessica's elopement and the theft of his gold, he mocks Shylock mercilessly by imitating his (supposed) response: "'My daughter! O my ducats! O my daughter! / Fled with a Christian! O my Christian ducats!" (2.8.2). This frenzied outburst makes Shylock out to be an unstable guy and a lousy dad who values his money far more than his daughter.
Yet, a few scenes later, when Shylock speaks with his friend Tubal about Jessica's theft of the ring, Shakespeare shows us another side of Shylock:
Out upon her! Thou torturest me, Tubal: it was my
turquoise; I had it of Leah when I was a bachelor:
I would not have given it for a wilderness of monkeys. (3.1.14)
Here we learn that the ring was given to Shylock by his dead wife, Leah (Jessica's mother). We also find out that it means a great deal to him not because of its monetary value but because of the sentimental value he attaches to it. Shylock's grief-stricken response to the news that Jessica traded the ring for a monkey is touching and quite human, don't you think?