Sewant is the black and/or dark purple black shell bead system of the 17th century in Nieuw Nederlandt

New Netherland

New Netherland, or Nieuw-Nederland in Dutch, was the 17th-century colonial province of the Republic of the Seven United Netherlands on the East Coast of North America. The claimed territories were the lands from the Delmarva Peninsula to extreme southwestern Cape Cod...

 of what is currently the States of New York, New Jersey

New Jersey

New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...

, Pennsylvania

Pennsylvania

The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...

, Connecticut

Connecticut

Connecticut is a state in the New England region of the northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, and the state of New York to the west and the south .Connecticut is named for the Connecticut River, the major U.S. river that approximately...

, and Delaware

Delaware

Delaware is a U.S. state located on the Atlantic Coast in the Mid-Atlantic region of the United States. It is bordered to the south and west by Maryland, and to the north by Pennsylvania...

. This fiat currency system was introduced to the English at Plymouth Colony

Plymouth Colony

Plymouth Colony was an English colonial venture in North America from 1620 to 1691. The first settlement of the Plymouth Colony was at New Plymouth, a location previously surveyed and named by Captain John Smith. The settlement, which served as the capital of the colony, is today the modern town...

 Plantations in 1627. One black Sewant is equal to two white wampum

Wampum

Wampum are traditional, sacred shell beads of the Eastern Woodlands tribes of the indigenous people of North America. Wampum include the white shell beads fashioned from the North Atlantic channeled whelk shell; and the white and purple beads made from the quahog, or Western North Atlantic...

. The sewant is tied to the stiver, denarius of England (penny or d.), ore, daler, real, livre. 20 stiver = 24d or 1 stiver = 1.2d.
Sewant is the Dutch rendering of what the Native Americans in the 1600s of what is now New York, Connecticut, New Jersey, Pennsylvania, Rhode Island, and Massachusetts called the purple and white parts of the Quahog shell when made into beads, used as money and trade between the Dutch, Native Americans, English, French, and other people.
The money was of the Dutch money system, and translated into the different European and Native American trade and money systems at the time, around 1620s to 1660s.