He entered the Sainsbury's Local store in Grayshott, Hampshire, shortly after 22:45 GMT on Saturday and threatened staff with a black handgun.
Police also said the man, who spoke with a local accent, wore two pairs of gloves - one black leather, and another "like washing-up gloves" on top.
An accomplice waited by the door during the raid, police said.
The men made off with cash from the tills and fled.
The gunman was described as white, about 5ft 7in to 5ft 8in tall, of small and skinny build, with tanned and weathered-looking skin.
He was wearing a grey hooded top, faded dark blue jeans, black heavy-duty work boots and a scarf over his face.
The second man was wearing similar clothing.
Three members of staff and a customer were in the Headley Road store at the time of the raid. No-one was injured.
Det Sgt Oliver Lage of Hampshire Constabulary said: "This is a very unusual incident in a rural community. It has obviously left those who were inside the store very shocked but thankfully uninjured.
He urged anyone with information to contact police.
An armed robber with a "croaky voice" is on the run after a gunpoint robbery at a supermarket, police have said.