My wife an I had a new quartz counter top installed in July.  In autumn the seam between two pieces expanded and if there was a sealant between the two pieces to also separated. With further weather change its now moved closer together.  I need to glue/seal this with something but I don't know what to use.  The gap seems to small for silicone calk.  Any ideas on how I fill/seal this?

Thanks,
Craig