Natural Spots on Natural Stone (black slate)

For our new bathroom in Germany we have chosen to use black slate tiles (type: Brasilian Rio Negro or Mustang, 60cm x 60cm x 1cm) for the flooring. We have them already since almost six years in our kitchen, our actual bathroom and guest toilet - and we are very happy with the quality and the look.

Today I learned that all the spots and marks on my new schist tiles - that I hoped can be somehow removed - have a natural background - as its a natural stone.

I never thought that the brown spots and the brown 'scratch' might be from iron accumulations. (We have not had this before). Even the brown big spot that looks like from a foot print is not from rubber band or chewing gum, it is natural! Again iron. Also the spots that look like some acid had dropped on one tile are apparently 'natural'.

The answer from the craftsman surprised me that much - well, I ordered natural stone, so if it's natural, everything is fine - that my brain got totally blocked and I did not say: well, I did not order multicolor schist tiles (I found them via google later today) or better: this tile would not pass quality control, if I would be in charge for purchasing in your company...

On Monday the natural stone tiles will get an impregnation with special schist oil. I am afraid that the spots might pop up even more - the craftsman said no.

Or should I see it from the other side: Lucky to have some special natural stone tiles, with iron accumulation ? Almost as exciting as a snail fossil ?

My recommendation if you use natural stone in a relatively small area:
- lay out all the tiles in front of you,
- cleaned of course with a wet towel,
- and choose one by one regarding the texture and colour and maybe not so beautiful spots,
- which one you want to have in front and which one you prefer hidden e.g. under a sink.
- Especially schist tiles (Schiefer Fliesen) are delicate among the natural stone tiles (Naturstein Fliesen) as cutting and laying them is not easy at all. So take the most recommended and experienced floor tiler (and even this is no guarantee for surprise free flooring!)

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UPDATE:

The story took another turn today (4th Feb).

After not feeling happy with the slate tiles and talking to a lot of people - including some experts and our architetto - we wrote to the company a letter (copied to the owner).

This morning the owner and the middle man (who told me that everything is natural) came to my house for further inspection of the flooring. The appointment was settled at 7 am because I wanted my husband to support me (somehow some workers seem to respect 'housewife's' ideas less).

The owner was charming and sovereign, no need to explain much, he saw the situation and he saw our other slate floors and then decided to exchange 4 of the tiles. However not all of the claimed ones, as the iron spots can be cleaned with an iron sponge (why didn't the middle man solve the problem that way in the first place?). Two tiles that will be taken out have micro fractures and two have major damages (splitting-offs) at the borders. One of the damaged tiles is the one that has lots of strange spots. So I am very very relieved !!! Although there will be a delay of the finishing of the bathroom and more dust. But I am happy.