The penis shaped objects are made from volcanic black glass - known as obsidian - and are at least 3,000 years old, but could be up to 6,000 years old.
That dates back to before the Lapita people, and could shed new light on the history and origins of the the Pacific region's ancient civilisations.
Dr Robin Torrence, Senior Principal Research Scientist at the Australian Museum, told Bruce Hill its unknown what the hand crafted artefacts were used for, but what is clear is that they are very special.
Presenter: Bruce Hill
Speakers: Dr Robin Torrence, Senior Principal Research Scientist at the Australian Museum
TORRENCE: For one thing, they're very, very big, they're 20 centimetres long, they're very flat and they're sharp, but the edges, if you look under a microscope, you can see they've never been used. The thing is that they're so thin and flat and sharp, that if you tried to use them for anything they'd break. So right away, you know you're not dealing with a kind of functional utilitarian tool. But the other thing is they look identical to a penis. Mind you it's a flat penis, it's a profile of a penis, it's not a 3D view. And this was done by a very clever way of manufacturing by hitting a blow just across the front of the tool to give this very, very distinctive shape. So we think given the size of these things, the fact they're made out of a rare stone, called obsidian, they're shiny, they flashy, they have a really distinctive shape, that these were a very special artefact for people in the past.
HILL: Now obsidians basically a kind of volcanic glass that can be very, very sharp and keep an edge, but it's also very brittle. I know it was used in Mesoamerican civilisations a lot, but from what you're telling me about this, these were not knives or arrowheads or spearheads. These were ceremonial objects?
TORRENCE: Yes, that's right. Although this tool is heavily worked, it has a lot of what we call retouch on it to give it its shape, so somebody's put a lot of work into it. It's so thin, that if you try to do anything with it, it would just smash and as I say, by looking at the edges under high powered microscope, you can see that there's no damage to it, so it wasn't used. It's also kind of too fat, to wide to hold in your hand, so the bit that is the handle, just it doesn't feel right. It's much more likely that something this big and flashy was there to catch attention and the clearly manufactured shape is sending some messages out to people.
HILL: How old are they?
TORRENCE: These are older, we know they're older than a volcanic eruption, which is about 3,200 years old, because they're always found tools of this shape, found under volcanic ash of that age. We don't know how old they go, but we know they're under another volcanic ash 6,000, so they're at least between 6,000 years and about 3,000 years old.
HILL: Well, if these were thousands-of-years-old, they would have obviously been in the ground for a long time. How did we come to actually make this discovery, that they were actually there?
TORRENCE: OK. These particular tools that we're just reporting on today were discovered by a bulldozer.
HILL: That's a fairly crude tool of archaeology?
TORRENCE: It's a very crude tool of archaeology and fortunately, there was some wonderful workmen, who saw the flash of black and they know from their pasts that that stone was part of their ancestors youth, so they stopped the bulldozer and they called the manager and they said this tool is thousands-of-years-old.
It was a big joy to me, because it means my work. They obviously, the words getting around and then they called me in Sydney, and I made, they stopped all the work at the site and I and my team made a trip up there. Unfortunately, the whole site had been destroyed by that stage, but between the workmen and us we found bits of five more tools, identical tools, so there was a little cache of probably six tools and the area was about 50 square metres, something like that.
HILL: It must be really exciting to hold something that old, because I know that it's very difficult for archaeologists in the Pacific to find any relics, apart from pottery, in this case, volcanic rock. Do we know anything about the people who would have made these obsidian palaces, were they ancestors of Melanesians, Polynesians, some other people entirely?
TORRENCE: Ah, I assume they're the original ancestors of the Melanesians, absolutely. I can't say a great deal about the language they spoke, because language isn't represented by archaeology. But the stem toolmaker's were there certainly from 10,000 years ago and making these tools and lasting for 5, 6, 7,000 years. So it's a long tradition.
HILL: What will happen to these objects now?
TORRENCE: We left them on the plantation. We took a portable XRF machine to measure the geochemistry and a portable microscope to measure the edge damage and since we left, the manager has taken the tools to its rightful place at the National Museum of Papua New Guinea. So everything that I discover or excavate in Papua New Guinea, is some of it might be borrowed for awhile to the Australian Museum, but it all goes to the National Museum in Papua New Guinea as part of their heritage.