What are Those White Dots on my White Marble?

Frederick M. Hueston, Stone Forensics

Have you ever wondered what those white dots are on white marble? You see them in lobbies where there are thousands of them. You can see them, but you can’t feel them. What are these mystery dots?

If you take a hammer and hit a piece of white marble, it will leave a white dot. Stone Restoration contractors will try to grind them out only to find that they are very deep. In many cases they are deeper than they are wide. What is these mystery white spots?

Professionals will call them Stuns or Crystal Fractures.  I have explained these as a explosion of the calcium crystal within the stone.  To verify my theory, I reached out to Kendall L. Hauer, Phd, Miami University, Department of Geology and Environmental Earth Science and here is his explanation:

When any color of marble/limestone is crushed, it will take the form of a white powder. Essentially, what you are seeing is the “streak” of calcite, which is always white. It is always white because powdering limestone essentially negates the effect of any color-causing impurities. Wikipedia’s entry on mineral streak puts it this way: “Small amounts of an impurity that strongly absorbs a particular wavelength can radically change the wavelengths of light that are reflected by the specimen, and thus change the apparent color. However, when the specimen is [powdered] to produce a streak, it is broken into randomly oriented microscopic crystals, and small impurities do not greatly affect the absorption of light [of these crystals].”

 So, in otherwards. The impact a sharp pointed object, such as a women’s high heel will crush the calcium crystal leaving a white dot. Now you know.

Or here is another way to look at it.

When stun marks or bruises occur on the surface of white marble, the impact or pressure applied to the marble causes localized damage that affects the crystalline structure of the stone. Marble is composed primarily of calcite or dolomite minerals, which form interlocking crystals.

During an impact or under pressure, the force is transmitted through the marble, and the crystalline structure undergoes deformation. The crystals within the affected area experience compression and displacement, resulting in the formation of small indentations or depressions on the surface.

The compression and displacement of the marble crystals disrupt their original arrangement and cause them to compact and rearrange in response to the force applied. This compaction and rearrangement of the crystal structure creates the visible indentation or depression on the marble surface.

As a result of the deformation, the physical and optical properties of the marble crystals can change within the stun marks. This alteration in the crystal structure leads to a lighter color compared to the surrounding area. The compacted crystals may scatter light differently or reflect it at different angles, resulting in a perceptible difference in coloration.

The extent and severity of the damage to the marble crystals depend on the intensity of the impact or pressure applied. Stronger forces can cause deeper indentations and more significant disruption of the crystal structure, resulting in more pronounced stun marks. On the other hand, lighter impacts may cause shallower indentations with less disruption to the crystals.