From today's NY Times: http://www.nytimes.com/2016/04/02/business/popular-quartz-countertops-pose-a-risk-to-workers.html

As
sleek “engineered stone” countertops grow in popularity, safety experts
are warning that workers who handle them are at particularly high risk
from an old workplace hazard — silica, the mineral tied to silicosis, a debilitating and potentially deadly lung disease.

The
countertops are made from processed quartz, a material containing
silica levels as high as 90 percent, or twice the amount found in
marble.

When
slabs of engineered stone are cut and finished to fit a kitchen or
bathroom, large quantities of silica particles are released. If workers
inhale them, it can start a process leading to silicosis as well as to
lung cancer and kidney disease.