Hey...don't take my word for it, I'm only speculating. Get it...speculating. lol
Maybe the folk at your clearing firm are believers in the healing powers of quartz, the most common mineral(SiO2) on the planet and would consider it of great value. After all they could scam a great many people with 200 pounds of quartz.
On a somewhat serious note...check that chunk-o-quartz for gold. It is not uncommon for gold to be found in quartz.