Tell me more about "Muslim Rosaries"

I took a cab into the office today, and the driver had an ornately decorated string of white beads hanging from his rearview mirror. There were brightly colored orange, yellow, and green yarn tassles hanging from it as well. When I asked him what it was, he described it as a “Muslim Rosary”, and that the white beads were made from elephant tusk. He said it was worth quite a lot of money, and that his older brother should be the member of the family to have it, traditionaly speaking (oldest male in the family has it) but his brother had given it to him.

Googling I found that they are called sibhahs or tasbeeh, and that they are used when reciting the 99 speakable names of Allah.

Can any Dopers flesh-out this bare-bones understanding of this item?

I have my doubts that many Muslims are thrilled with the term “Muslim Rosary”, but I heard it from a Muslim first…

I’m also curious as to just how much it would be “worth” if it was indeed made of elephant tusk and as old as he said it was.
I don’t know how old, but he said it had been in his family for a “very very long time”.

I’m also curious if there are other materials used to make them?

I have my doubts that someone would actually hang such an item from the rearview mirror of their cab, but maybe that’s just me.