Hi All ~
Jurassic Reptile Sand is NOT silica based. The sharp edges of any silica sand are the culprits when it comes to impaction! If I recall correctly, JRS is composed entirely of smoothly rounded quartz crystals.
At least in the past Jurassic Reptile Sand was available from Jerry Bergosh in Utah in 50 pound bags and smaller.
Just a caution for you all: My first mature female Oedura castelnaui prolapsed on a substrate that included only JRS and peat moss. Several months later she prolapsed a second time. She recovered, but had to be seen immediately at the local vet emergency room. After the reinsertion of the tissues, her treatment consisted of a diet of only chicken baby food for about two months, catlax applied directly to her lips only once a day, and a short tepid water soak once a day till she passed the sand. She still thrives today :-]
I still use a 50/50 combo of JRS and cocopeat in the Oc nest boxes, but have steered totally away from any sand in the Oc substrate. Right now I am leaning towards 100% cocopeat fiber for the Oc substrate.