Type POINT and index

Hi All

I made this little talbe:
CREATE TABLE location (
loc_id SERIAL PRIMARY KEY,
cordinata POINT NOT NULL
);

I want to index the column "cordinata" with "RTREE" so I can scan it fast
and find easily distance or other GIS information.

When I try to index the column it keep asking me about operator, which
should I choose ?

I need thing like: select all other coordinates that are in Radius of 100
units.

Is it possible ?

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