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Although the particle size distribution and coloring processes are of crucial importance, the selection of the natural stone itself is in fact just as important. Several characteristics are essential when analyzing and selecting an appropriate and suitable stone. The main qualities that are required are hardness, opacity to UV sunlight and the amount of iron content. In other words, an acceptable stone for granules must be durable as well as opaque and rust-resistant.

A suitable stone must be sufficiently hard, otherwise once coated the natural stone could break apart or even fracture during the manufacturing process or by roofers and homeowners walking on the shingles during or after their installation. The majority of natural stones are simply too soft to be suitable for colored roofing granules. Fragile stones such as calcite, dolomite or slate would break apart which would lead to exposure of the uncolored interior portion of the stone and possibly to premature mineral granule loss.

A third but equally important characteristic is the degree of iron content found in stone. To be suitable a stone should have only a small amount of iron in its composition. This to prevent iron from leaking out from granules, which can lead to rust stains on a roof.

There are several factors that can cause granules to loosen and be removed from bitumen roof shingles.

• Cleaning the roof with high water pressure can blast granules from roof shingles.
• Extensive winds, storms or heavy rainfall can also be factors
• Small hail can displace roofing granules.
• Any foot traffic can cause granules to remove.

• It is not a mistake if a couple of granules appear after a storm if your roof isn’t that old. But if your roof is old and most of the granules are peeled off, you should consider replacing it as this can be a big concern.
• The easiest way to do this is to be physically on the roof and check the asphalt shingles. If you see many spots without granules and there is only the top coating of bitumen left, it could mean that it’s time to replace your shingles.
• Remember that regular maintenance and inspection of your roof will extend its life by many years.

Roofing granules are made from crushed stone and minerals. With today's advanced manufacturing techniques, these granules allow roofing manufacturers to create asphalt shingles of virtually any color, size and shape. These small colored stones are one of the most important parts in the composition of asphalt shingles together with bitumen as well as the supporting inlay from fiberglass. Learn more about the shingle production process.