How to setup hook_install to have a geometry field on a POSTGIS database?
I have no idea if this will work (don't have a postgis install handy to test), but try

$schema['table'] = array(
  'fields' =&gt; array(
    'some_geom_field' =&gt; array(
      'pgsql_type' =&gt; 'geom',
      ...
    ),
  ),
);


If that doesn't do it I think you're out of luck using hook_schema(), you'll probably need to execute a custom SQL script instead.