Hello slate people
Some types of slate occasionally display on their surface a circular/ellipsoidal carbonate mineral, usually of white to yellow color, known as “flowers” or “rosetta” (Italian for rosette). Carbonates are one of the commonest mineral groups on Earth, and can be found in virtually any place of this planet. They are a key component of the shells of marine organisms and corals, and the main constituent of numerous rocks such as limestone. Actually, carbonates form part of our dairy diet, since they are main source for calcium, one of the main elements forming our bodies. But, how these carbonates got on the surface of our slates? Sometimes, once the slate is completely formed and while it is still on the rock massif, before quarrying, underground water may flow across the rock. Usually this water has carbonate dissolved, together with other minerals. The carbonate can then be deposited among the slaty cleavage planes. The mineral grows from a spot, expanding inside out, like a blooming flower. These carbonate flowers can measure from a one to several inches, and appear on the surface of some slate shingles. Are they really a problem? Not at all. These carbonates are very unstable under normal environmental conditions, since they cannot withstand slightly acid conditions, such as those created by rainwater. So if you find these carbonate flowers on your roof, do not worry. After some months, perhaps a couple of years, they will just rinse off. On the other hand, if you are in a hurry and do not want to wait this time, or just want to get rid of them, you can use a common slightly acid component, cheap, easy to find and completely secure for human and environmental health, vinegar. Just brush gently the flowers using vinegar, and they will quickly disappear. Easy and safe.
Víctor Cárdenes Van den Eynde
File caption: Here you can see a couple of carbonate flowers before and after rising with vinegar. I submerged in vinegar just part of the carbonate so you could easily see the change. HINT: do this after a hot summer day, when the slates are hot. Heat favors the reaction, so it will be much easier to get rid of the carbonates.