One aspect or lighter colored granite is that there’s a higher concentration of crystalline minerals such as quartz, and darker colors indicate the presence of biotite minerals. When granite tiles or slabs have a high content of feldspar and biotite, their appearance recalls a batch of cookies and cream. Dark spots can be part of the veining patterns of granite. In this case, they look organic and designed in a manner that only nature is capable of. In other cases, unnatural dark spots on granite are caused by external factors that need to be addressed.
Dark Spots Right After Installation
When this happens, and it’s usually on the day following installation of granite countertops, the problem is related to the adhesive and accelerant used by the contractors. Using too much of the wrong adhesive on white granite slabs can result in globs bleeding from the underlayment up to the surface, which is something the installer must inspect and repair.
Granite isn’t resistant to water staining, and it’s not completely stain-proof. If your granite counters are routinely exposed to water, dark spots may appear if the surfaces aren’t frequently sealed. You can test the strength of your granite’s seal by pouring water, about 3 inches in diameter, on the surface and letting it sit for 30 minutes. Make sure to do this in several locations, since the integrity of the seal could vary from area to another. If the water beads, then the stone remains sealed. However, if the stone is penetrated—look for a dark mark or ring created by the water—it’s time to reseal. Check for etching and stains as well before sealing your stone surfaces. You’ll want to fix these issues before the granite sealer is applied.
Wine, Vinegar, Coffee, and Tea Stains
Many plants and fruits contain anthocyanins, natural substances with pigmentation properties that are just waiting to chemically react with the molecular structure of granite surfaces. If you spill wine on the granite countertop in your kitchen, you can expect a dark stain to form if it isn’t cleaned quickly. Surface stains, those that appear on top of a strong seal, are easy to wipe away with a high-quality granite cleaner. Deeper stains that penetrate the pores are more difficult to remove, and they’re more likely to occur when the stone surface lacks a strong seal. White wine can also stain granite, but it may take longer for you to notice. When it comes to removing organic stains such as these, try taking a paper towel, cotton balls, or a white terry cloth towel soaked in liquid bleach and placing it on the stained area. Allow it to sit for 24 hours, then rinse with water.
Whether they’re caused by vegetable oil in the kitchen or synthetic oil in the bathroom, these stains can turn into dark spots rather quickly. To remove oil stains from granite, mix baking soda and acetone into a thick paste, enough to cover the entire oil stain, and leave it for 24 hours. Rinse with water and remove all remaining paste before applying a fresh coat of sealant.