We just got another of those cut clam shell pearls a couple of months ago. People think they are valuable because of the Pearl of Allah scam. That pearl acquired an outrageous price over the years, but in tracing its value, it was stolen from the Pisi family of Palawan in about 1939. The con man who took it under false pretenses took it to New York and put it in Ripley's "believe it or not" museum with a 1939 price tag of $3 million. The thief died without selling it, then another couple of slick guys bought it for $200,000, but only paid a fraction down ($3-5k) until it was sold for 30,000,000. It has never been sold again, though the pearl cartel's members jacked the price to $63,000,000 they did sell portions to others in weird partnerships, one of who had his wife murdered by a hitman recommended by a member of the pearl cartel.
The main guy died, the pearl has disappeared. Since only 3-5 grand was ever paid for it, it is worth $3-5,000, theoretically, but $0 in reality, since there never has been a buyer for it. It is a scam. and the pearl above is a scam too. It does not look like a pearl, but like the shell.
Your should read the story of the Pearl of Allah on this website, then take the hunk of shell straight back to the sellers. At least look at a photo and you will see that a Tridaca gigas pearl looks like a brain, while yours looks like a brick.
I am so amazed that people still want to perpetuate a myth that those gigas pearls are worth anything- well they are worth the value of the shell if they are attached.