I tried for the first time this uncommon fruit called Gal Siyambala which means Pebble Tamarind or Sri Lankan Velvet Tamarind Seed. There is another variety of tamarind seed called Gaduguda (light olive green) that I haven’t tried it yet.

Velvet Tamarind is so common in the season that you don't need to leave the car to buy them
Velvet Tamarind by the roadside.

Gal Siyambala seen once a year between August and Novemenr and it’s considered to be as a fast food, nibble on the run. When the season starts you can see this fruit on the street markets in cities, towns and in stalls by the roadside.

The velvety shell of the seed is brittle and cracks quite easy between the fingers revealing powdery palp. It has an acidic taste which is similar to Tamarind but it is sweeter, drier and more powdery. For me the taste was highly addictive.

According to Dr. Nirmala M. Pieris, it comes with quite a number of health benefits since it consists of fibre and is also rich in vitamin C, vitamin A, thiamin, folic acid, riboflavin and niacin. 

Lowers cholesterol
Prevents constipation and is a good diuretic
Boosts immune system
Maintains good metabolism
Regulates cell functions
Nourishes skin
Fights harmful micro-organisms
Benefits of Velvet Tamarind (Feel free to share)

I will also highlight that it may help in relieving toothaches and improve oral hygiene. And not only that, some people in Sri Lanka and temple caretakers use the fruit pulp to polish utensils, shrines statues and oil lamps.

Sources

Links

http://www.sundaytimes.lk/171119/mediscene/that-rare-velvety-marvel-268754.html
https://www.fruitsinfo.com/velvet-tamarind.php
https://drhealthbenefits.com/food-bevarages/fruits/health-benefits-black-velvet-tamarind

Scientific Name

Dialium Guineense