The small, triangular jade blades found in Antigua are relics of the Saladoid culture, a society named for its home region along the Orinoco River in modern-day Venezuela (See map of Venezuela).
Known for their elaborate pottery, the Saladoid spread to Caribbean islands as far north as Puerto Rico by 500 B.C.
Archaeologists have excavated jade items in the West Indies before, but the source of the jade has been a puzzle, Harlow explains.
No jade deposits are known to exist in the eastern Caribbean. Also, many archaeologists have held that the Saladoid were insulated from the wider world, their travels limited to short canoe trips between islands.
Harlow says the jade used to make the Antigua blades is of a distinct, very hard form called jadeite.
Only a dozen jadeite surface deposits are known in the world, including a vein on the north side of Guatemala's Motagua River Valley, he adds.
But until recently Guatemalan jade deposits did not match the Antigua jade or other, high-quality forms found in some Maya tombs.
Then came the devastating rains of Hurricane Mitch in 1998. Violent runoff brought chunks of extremely high quality jade careering down the rocky gorges on the south side of the Motagua River.
"As soon as we heard about that, we started looking for its source," said Harlow, a veteran of previous work in the region.
His team found jadeite there of a quality beyond anything recently mined in Guatemala, he says.
The samples they brought back came just in time to answer questions about the Antigua jade pieces.
Shortly after the new deposits were discovered, Harlow received the Antigua blades, dated from 250 to 500 A.D., from the late University of Calgary archaeologist Alfred Levinson.
Harlow says he immediately suspected that the axe blades were from the newly confirmed deposits, based on the jade's unique composition.
He compared the texture of both the Antiguan and Guatemalan jade and measured their ratios of minerals such as mica, albite, omphacite, and quartz.
Harlow found that the newfound deposits and the Antigua pieces bore the same distinctive quartz grains, which are absent from jade mined anywhere else, he says.
"If that [Antigua] stuff is not from Guatemala, the fates are playing some kind of game," Harlow said.
Proof of Trade?
Among those welcoming the finding is archaeologist Richard Callaghan of the University of Calgary, who was not part of Harlow's team.
He has studied remains of early Caribbean island societies for decades. He says the discovery provides new evidence of long-range trade in the pre-Columbian Caribbean.
Based on his research of Saladoid pottery and other artifacts, Callaghan believes that the civilization was sophisticated enough to maintain organized, long-distance contact with other cultures.
"I think those guys could go by boat straight from Puerto Rico or other islands all the way to [Mexico's] Yucatán [Peninsula]," he said.
The trade routes were most likely traveled by big, seaworthy canoes, Callaghan says. The vessels may have resembled the dugout logs seen centuries later by Spanish explorers.
Such seafaring ability, Callaghan adds, may have persisted well after the Saladoid culture faded around A.D. 1000.
The culture was replaced by Caribbean peoples collectively called the Taino, whom the Spanish later conquered and all but exterminated.
Murphy, the Antigua curator, shares Callaghan's expansive view of the Saladoid's cultural reach.
Murphy hopes the jade-axe findings may spur further study into the origins of other exotic, elaborately carved stones found among Saladoid relics.
For example, he says, some Saladoid artifacts are made of a type of turquoise not known to occur naturally anywhere in the Caribbean.
"It could have come all the way from Chile," Murphy said.
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