I came across this site which is a virtual fossil museum and was curious to see if they had any microbial specimens. They did and interestingly enough there were some pictures of these stromatolites found during the Lower Cambrian that looked like pisolites. I must not be thoroughly exposed to all types of stromatolites since some of these pictures confused me. But I guess that is the nature of nature. It is complicated. What seems to be a pisolite is in fact a stromatolite. But who's to say that you cannot call it a pisolite too? It's spherical, has a nucleus and cortices, and is wider than a mm. So the only difference is that bacterial matter created the cortices around the nucleus instead of by mechanical/physical processes. That is, if this is actually a stromatolite.
So here's the link to that picture: http://www.fossilmuseum.net/Fossil_Galleries/Stromatolites/Stromatolite461/DS461g.jpg
Here's the link to the website: http://www.fossilmuseum.net/Fossil_Galleries/StromatolitesAmerica2.htm
There are some other questionable stromatolite pictures in this website. I am not sure about the credibility of the website or I maybe ignorant!