Although quartz is not a renewable resource, it's also not exactly in short supply?it is the most common mineral in the earth's crust. Just because quartz is plentiful, though, doesn't mean that engineered stone is an environmentally sound choice. There are serious concerns about ecological damage to mining sites and petroleum use in mining and fabrication.
Engineered stone countertops are made of about 96 percent quartz, combined with acrylic resins that are petroleum byproducts. They also contain alumina trihydrate fillers made from bauxite ore, which is mined primarily under toxic conditions in developing countries. (Companies like Alcoa have committed to improving the conditions of mining sites.)
Engineered stone does have some pluses. Like granite, it is incredibly durable and will last a lifetime. It has an advantage over granite in that it is nonporous and resists bacteria and mold. Also, Zodiaq, Formica, Wilsonart and Silestone have been certified by GreenGuard as low emitting (look for the GreenGuard seal).
Still, I would recommend locally mined (within 500 miles of your home) or salvaged slabs of natural stone, simple concrete counters (with fly-ash) or counter products manufactured from renewable or recycled materials, which have a lower embodied energy than most engineered stone counters on the market.