Does anyone have adjacency data for the census block groups?

Does anyone have adjacency data for the census block groups? I would like to know which are neighbors. I’ve tried to import the geojson file into R, but geojsonio doesn’t like that file

@Martin_Andersen_UNC_Greensboro one tip:

the CBG 12 digit fips is hierchical. So all CBGs that have the same first 11 digits are part of the same census tract, and therefore are all close to each other. Similarly the first 5 digits are all part of the same county and first 2 digits are all the same state.