Bulk 1 1/2" - 2" Gray Granite (#4)
Gray granite is excellent at reducing water loss due to evaporation due to its ability to reflect sunlight instead of absorbing the heat. A secondary effect of reflecting sunlight is that when weed seeds find their way onto soil in your landscape and germinate, they will likely not survive because they cannot reach enough sunlight.
Due to the nature of natural products, physical properties will vary (size, color, etc).