These marbles are usually brown or yellow because of the presence of iron oxide.
Marble with iron oxidation.
When exposed to water acids or bleach the iron in the stone will begin to oxidize and turn it yellow.
This oxidation process is accelerated when the tile is saturated as in the flood in the above example.
The most common culprit for white marble turning yellow is iron which can be found in many natural stones.
Iron stains however can be eliminated by mopping away water as accumulated in the marble tiles in order to prevent the iron from getting oxidized.
The rust stain simply returns as moisture brings more rust back to the surface.
When exposed to water acids or bleach the iron in the stone will begin to oxidize and turn it yellow.
If you expose a brand new nail to water and air it will turn brown and rust.
This process of oxidation is similar to the rusting of metal.
Yellow brown stains in white marble like carrara marble are almost always due to the oxidation and rusting of iron deposits that are embedded in the marble as described in this article above.
This process of oxidation is similar to the rusting of metal.
The same process is occurring with the iron in the marble.
In extreme circumstances the marble can turn a brown color akin to what happens to a piece of iron left out in the rain.
In severe cases the process of oxidation is difficult to reverse or stop.
I highly doubt it has anything to do with light sensitivity.
Oxidation is responsible for yellow brown stains that look like they are coming from the inside out.
If you expose a brand new nail to water and air it will turn brown and rust.
The most common culprit for white marble turning yellow is iron which can be found in many natural stones.
Onyx marble was the alabaster of the ancients but alabaster is now defined as gypsum a calcium sulfate rock.
In extreme circumstances the marble can turn a brown color akin to what happens to a piece of iron left out in the rain.
This oxidation process is accelerated when the tile is saturated as in the flood in the above example.
Another cause is the proximity to iron metal which is oxidized by air in the.
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They are in the strict sense neither marble nor onyx for true onyx is a banded chalcedony composed largely of silicon dioxide.