I would guess it has to do with moisture-spent some years climbing on sandstone out west.

Moisture caused some types of discoloring but if I remember most discolorations were black and similar to what's on your stone.

Maybe it is lichen growth-interior or exterior?

Maybe you need a mildecide , fungicide, biocide product.

On Mon, Mar 30, 2015 at 9:46 PM, <hectorcastillo@comcast.net> wrote:

is the black in the grout ?

Hector Castillo
From: "Hector Castillo" <hectorcastillo@comcast.net>
To: sccpartners@stoneandtilepros.simplelists.com
Sent: Monday, March 30, 2015 5:21:36 PM
Subject: Re: Trying to figure out what this is

Try solvent for a test

Sent from my Verizon Wireless 4G LTE smartphone

-------- Original message --------
From: Mike Marsoun <nulifesc@bigpond.com>
Date:03/30/2015 5:02 PM (GMT-08:00)
To: sccpartners@stoneandtilepros.simplelists.com
Subject: Re: Trying to figure out what this is

Is that sandstone? I see that a lot. Nothing will take it out. I have tried pure bleach sitting overnight. Nada.

Sent from my iPhone

On 31 Mar 2015, at 9:07 am, Stephen Webb <stephen@newlifemarblerestoration.com> wrote:
Peroxide did nothing, It's chiseled sand stone and these spots are on random tiles here and there with no connectoin to plants etc. any thoughts?
Thanks
stephen

-------- Forwarded Message --------

Subject: What?

Date: Mon, 30 Mar 2015 10:57:07 -1000

From: Stephen <mauiwebbs@gmail.com>

To: stephen@newlifemarblerestoration.com

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Subject:	What?
Date:	Mon, 30 Mar 2015 10:57:07 -1000
From:	Stephen <mauiwebbs@gmail.com>
To:	stephen@newlifemarblerestoration.com

Regards,
Stu Rosen
201-446-1200

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