Agate is a Micro-crystaline (not big, gemmy crystals) form of quartz, and characteristically is at least partially semi-translucent. It is hard, takes a very nice polish, is tight-grained and comes in an amazing array of colours. In addition to its natural range of colours, it also takes dyes well and can be had in a stunning array of fashion colours. It often exhibits banding and flow patterns. It is formed in pockets left in lava, which over time, have filled with deposited minerals.
If you spot a trend on these pages that leads you to think that a disproportionate quantity of stones are some form of quartz - you would be absolutely correct. Quartz is the most abundant mineral in the earth's crust.
We try to choose consistent stock, but the nature of natural stones is that there will be inconsistency between strands and between individual beads.