No idea what "tenn silver" is...but it appears hand made....don't know if sterling or not...often craftsmen didn't mark their stuff as to silver content.
What part of the country did your grandmother live in? How old is/ was she? It doesn't appear to be very tarnished....how has it been stored?
Wondering if it is silver as silver tarnishes badly over time....and wondering if "Tenn Silver could be part of the artist's name.
It's lovely!.....no idea how you would polish it....for sure do NOT dip it....

I think this piece is hand made. I have seen examples of this sort of art in "Lapidary" and "Rock & Gem" magazines. The markings on the back of the pin seems hand drawn/scribed.

If this were a Swedish piece, and if this was silver alloy, the mark, B9, could be a date code that represents the year 1952. See table in link below.

http://modernsilver.com/Swedishhallmarks.htm

The remainder of the markings are a mystery to me. "Tenn" could be an abbreviation for Tennessee. However, there is a trade publication that contained the term, tenn & silver. It is the name of a Swedish company and It operated from 1944 to 1982. See link below:

https://antiquesilver.site/price-guides-publications/1958-swedish-sterling-silver-trade-catalog-tenn-and-silver-tesi-goteborg_362030436049.html

Thank you both, my grandmother was born in Worcester, MA and lived in Buffalo, NY ... born in 1901, lived for 94 years. I've had this since she passed in my jewelry box.

jemdandy, interesting about the Swedish connection ... I also have 2 pieces made by Sporrong in Stockholm. I sent them a picture of another brooch I have (below), but their records only go back to the 1990's and they couldn't give me any information about it. My grandparents had close friends that lived in Stockholm, and we're part Swedish.

Here's a brooch with similar design elements to your "cattail" brooch.

http://www.ebay.com/itm/Vtg-Sterling-Silver-Granit-Co-Finland-Modernist-Scandinavian-Pin-Brooch/253146342004?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20140107094819%26meid%3Db6b75cd47e724bf383f135fcc536e12f%26pid%3D100039%26rk%3D1%26rkt%3D4%26sd%3D253146342004&_trksid=p2054436.c100039.m2059