Apple Isle Prospector


Tasmanian mad about fossicking and prospecting, specialising in sapphires and gold.


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Petrified Wood in Tasmania

Petrified wood is a common material in gravel beds and ancient river channels in Tasmania in the Tertiary between 66 and 2 million years ago. It’s particularly common in areas with Tertiary basalt flows.

How does petrified wood form?

There are several ways by which wood can be preserved well enough to become petrified. The most common involve the original trees getting buried under large quantities of flood debris, or volcanic ash.

In Tasmania, volcanic activity was common during the Tertiary, and most of our petrified wood was formed from trees buried under volcanic ash and basalt (lava) during this time. Volcanic materials are very rich in silica. Wood that has been heated during a pyroclastic or basalt flow is probably mostly sterile, so it will not rot when it’s buried. Dissolved silica from the volcanic materials gradually replaces the wood, but often the grain is well preserved and very evident.

Opal or chalcedony?

The two main types of petrified wood are opalised and chalcedonic. In Tasmania, chalcedonic wood is much more common. This is wood that has been replaced by straight silica. Chalcedonic wood is the type you find at places like Lune River, Swansea, Tunnel Marsh, Tunbridge, Weymouth, many of the beaches around Hobart, and in quite a few other parts of Tasmania.

Opalised wood is also found in Tasmania, but only occasionally. Opal is a hydrated silica that contains as much as 20% water. It is softer than chalcedony. Opalised Casuarina trees have been found in the Bushy Park / Macquarie Plains / Plenty area, buried under Tertiary volcanics. These included an entire tree, twigs, branches and trunk, still standing where it grew before it was buried.

Petrified wood as a gemstone material

Petrified wood can be a very good gemstone material, but a lot of pieces are porous and almost chalky, and never take a polish. Highly silicified specimens take on a very good polish and make great slabs, specimens, and cabochons.

Pebbles of petrified wood that are common in many Tasmanian beaches can be very colourful and often take a great polish.

Via Apple Isle Prospector: https://www.appleisleprospector.com/petrified-wood-in-tasmania/

Discovering Penguin Jasper

One of the great geological treasures materials you can find in Tasmania is Penguin Jasper.
While jasper is a fairly common gemstone, the coast between the towns of Penguin and Ulverstone in north-western Tasmania is a particularly good place to find high-quality stones. There is even a dedicated Fossicking Area in Penguin, which is a great place to get started, and where you can still find some great quality material. Given how good the fossicking is in Penguin, I was surprised that it was actually pretty hard to find any information about it online, so here’s my go at fixing that.

Access

The place to look is the cobble and gravel beaches in a piece of rocky coast between Tea Tree Point and Penguin Point, just to the east of Penguin, on the road to Ulverstone. You can find jasper boulders and cobbles at the steep, back part of the beach, near the high tide line.

The Penguin Fossicking Area is just east of Penguin, on the road to Ulverstone. The main collecting locations are on the beaches between Tea Tree Point and Penguin Point.

Because it is a designated fossicking area, anyone can fossick there and no permits are required. Please abide by the conditions set out in the Fossicking Areas in Tasmania booklet.

Parking can be tricky around the area. If you’ve never been before, it pays to do a drive-by or two beforehand to see where the few available spaces are,  being mindful of private property and people’s driveways. There is a large space of the uphill side of the road, opposite the railway tracks, with enough room for 2-3 cars, right near the main area. If you have a GPS, the coordinates are -41.12146, 146.11124. Cross the road and railway tracks, and about 50 meters west of the carpark there is a sort of a track to get down to the beach.

What does Penguin Jasper look like?

Jasper cobbles in shades of yellow-cream to red and purple. They often hide under basalt cobbles. They range in size from pebbles to large boulders.

The main material that makes up the beach is a dark basalt, sometimes full of holes. Among the basalt, cobbles of Penguin jasper stand out from their cream, reddish or purple colour. A lot of the better quality material hides under the surface boulders, so it pays to look carefully and move a few rocks around. A lot of the pieces of jasper have little bubbles or cracks running though them. They’re very beautiful, but not as good for lapidary. It pays to look around for a while and find solid stones. You’ll be able to tell the better quality ones because they’re heavier. They look and feel much more solid.

Good quality pieces range from small pebbles, good for tumbling and not much else, to large boulders the size of washing machines. Sometimes good pieces are on the darker side, and they camouflage well among the basalt. Visiting during a rain shower makes the jasper really stand out. The best pieces I’ve found are a pale cream background with red and purple blotching and veining, or darker purple or red with contrasting pale-coloured veins.

A piece of Penguin jasper, before and after polishing

Watch out for the blue-rings!

The coast in this part of Bass Strait is a classic locality to find blue-ringed octopus, and they’re very common under the coastal rocks in the Fossicking Area. Take care when turning over rocks in the water, quite a lot of them have a resident blue-ringed octopus. Gloves are a good idea. Needless to say, please don’t touch them, their bite IS painless, but deadly within a few minutes if untreated.

Here’s one we found under a piece of jasper we turned over:

 

I hope you enjoy fossicking in Penguin!