Writing CSV file from Array

I need to put double quotes around String objects from the array, but
not around other types of objects. :force_quotes puts double quotes
around every field. I don't want that. What is the best way to do
this? For example...

a = [["joe","cool",19,1000], ["mary","jane",20,5000]]

CSV.open("new_file.csv", "w", {:force_quotes=>true}) do |csv| a.each
do |r| csv << r end end

gives us this in the csv file:

joe,cool,19,1000
mary,jane,20,5000

I need this:

"joe","cool",19,1000
"mary","jane",20,5000