how to find a bimodal distribution

If I have a list of values in an Excel spreadsheet (fewer than 100 values) that I think may include a bimodal distribution, how can I easily test this theory and find the center of the two modes using Excel? To be more specific, I have measured grain size in a polycrystalline material and found a large stdev but my intuition tells me the grains fall in two size categories. is there an easy way to identify these groups and their peak values in Excel?
I am new to this forum. I'd appreciate any help.
Thank you!