Agate – TumbleStone

February-March 2022 Fossicking Trip: Stone of the Day #1, Birdlings Flat Banded Agate

For the last three years, I have taken a four-week fossicking trip to the South Island during the February-March period to find beach stones for tumble polishing. At this time, the beaches are no longer busy with people enjoying their summer holidays yet the weather is still likely to be mainly fine. I take about a week to make my way by car from Whanganui to Riverton, visiting some South Island east coast beaches on the way, such as Ward Beach, Timaru and Kakanui. I base myself for a couple of weeks at Riverton, visiting places like Gemstone Beach and Slope Point, before taking another week to visit east coast beaches on my return north.

This year, I left Whanganui on Thursday 10 February, crossing Cook Strait by ferry that afternoon. My first serious fossick was at Birdlings Flat the following day, Friday 11 February. I have not visited Birdlings Flat much lately, maybe only twice during the past two years. I arrived at 2 pm and spent a couple of hours walking from the car park to the sea and then northwards towards Banks Peninsula (and back). The most interesting stone I found was a small banded agate, Stone of the Day #1:

Stone #1.

With a torch behind the agate.

This stone has more white in it than previous banded agates I have found at Birdlings Flat (see for example the stone featured in the Monday 17 May 2021 entry in this Post) but its bands are well defined and it is a nicely smooth stone.

The other side of Stone #1

With a torch behind the stone.

The day was cloudy and dull, not good conditions for spotting agates. I saw only two others, non-banded. I picked up a small number of other stones, mainly jaspers and quartzites. There were very few people on the beach while I was there:

Birdlings Flat, from in front of the car park.

Closer to the northern end.

Getting closer to the cliff at the start of Banks Peninsula.

Some background about Birdlings Flat can be found here.

The next Post in the Series, on Stone #2 from Kaitorete Spit, is here. The Index to all the Posts in the Series is here.

FB Group Posts: 5, 6 & 7 June 2021 – Birdlings Flat Stone, Timaru and Moeraki Village Fossicking

This is the eleventh Post in this Series of my daily Posts in the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils”. The first Post in this Series is here.

Saturday 5 June 2021: Tumble-polished stone found on Birdlings Flat sometime over the last couple of years.

Other side of stone.

Sunday 6 June 2021: Three finds from my time on a beach just south of Timaru this morning. I am on my way south again to restock my beach stones for tumble polishing. My very first visit to this beach was yesterday, I just had to go back today, as there are some beautiful quartzites there. I also saw three seals. Right at the end, I came across a tiny fish (about 4 cms long) gasping for breath a couple of metres up the beach from the waveline – I carefully returned it to the sea.

I found a few green quartzites.

I’m hoping I can tumble this one in my 12lb barrel.

The beach just south of Timaru. I suspect recent stormy days have piled up more stones than usual – or at least given them a big stir.

The tiny fish I returned to the sea.

Monday 7 June 2021: Five small stones from my visit this morning to a beach near Moeraki Village, North Otago. Close inspection of each revealed fascinating details. Most are chalcedony (agate). The first three stones:

Stone 1 – small agate with “fortifications”.

Stone 1 held up to the light.

Stone 2 – orbicular chalcedony?

Stone 3 – another small agate.

It was difficult to see the details of these small stones before working with the photos. On the beach, I could often just see a hint of something interesting going on. Here is a photo of the beach, followed by photos of the other two stones:

The small beach near Moeraki Village.

Stone 4 – likely also to be chalcedony of some kind, maybe dendritic.

Stone 5 – conglomerate of some kind?

See here for the next Post in this Series.

FB Group Posts: 22, 23 & 24 May 2021 – Kakanui Jaspers, Agates and Quartz

This is the seventh in this Series reproducing my recent regular Posts in the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils”. The first Post in this Series is here.

Saturday 22 May 2021: Four small tumble-polished jaspers from a beach near Kakanui, collected in February-March this year, just out of the tumbler. 2 to 2.5 cms size. These illustrate just some of the diversity of jaspers from that beach.

The south end of the beach near Kakanui where I found these small jaspers.

Sunday 23 May 2021: Shining the light on (or through) three recently tumble-polished stones from a Kakanui Beach. Two beach agates (chalcedony) and one stained quartz.

Stone 1, beach agate (chalcedony) with cream-coloured markings, 3.5 cms long.

Another side of Stone 1.

Stone 1 held up to a sunny sky.

Stone 2, stained quartz stone, 4.5 cms long. The stone is actually very smooth and polished, not well conveyed in the photos.

Stone 2 with a torch behind it.

Other side of Stone 2.

Other side of Stone 2 with a torch behind it.

Stone 3, beach agate (chalcedony). 5 cms long.

Stone 3 held up to a sunny sky.

Monday 24 May 2021: Gorgeous jasper from a Kakanui beach – 5.5 cms by 4 cms in size. Found at 12.42 pm on 19 February this year (according to the time stamp on a photo I took of it then). The stone looked astounding on the beach. (See Day Three in this Post.) After tumbling, it has taken a very good polish, not shown well in the photos.

One side of the polished stone. It actually looks a lot better than this.

Other side of the polished stone.

Photo of the wet stone when found on the beach.

Photo of the wet stone when found on the beach.

The beach near Kakanui where the stone was found. Looking north towards Oamaru.

I started it in 400 grit and gave it only a week there before putting into polish. The end product has four or five small rough areas, which could have been smoothed away with more tumbling in grit but I wanted to keep its size and character. The close-ups don’t really do it justice. The photos taken on the beach when I found it are stunning and in many ways better represent how the stone looks now.

The next Post in this Series is here.

FB Group Posts: 18, 20 & 21 May 2021 – Birdlings Flat Beach Agate and Slope Point Stones

This is the sixth in this Series reproducing my recent regular Posts in the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils”. The first Post in this Series is here.

Tuesday 18 May 2021: Another recently tumble-polished small beach agate (chalcedony) from Birdlings Flat. Not banded this time. I decided to try to retain some of its outer character so did not wear away all of the brown and white material in the tumbler – and the result is very interesting. The stone is 3.5 cms long, having some small indentations but otherwise smooth.

One side of the polished stone.

Other side of the polished stone.

Held up to a sunny sky.

Wednesday 21 May 2021: This is the day I made a Post in the Group’s Alphabetical Series – “C” is for “Coral” – see this Post.

Thursday 20 May 2021: A small tumble-polished rhyolite from Slope Point (southern-most point of the South Island). Collected there on 3 March during a visit with Oliver Simpson [see previous Post]. Its wavy lines caught my eye on the beach.

It is a small stone.

One side of the polished stone.

Treasure

Another side of the polished stone, with a rough area apparent.

The beach near Slope Point on which the stone was found. To the right is the edge of a lagoon, with the open sea to the left (and ahead).

Oliver Simpson on the beach – many thanks to him for the day’s outing.

It has come out of a 3lb barrel this morning, my first completed batch of Slope Point stones. This stone is only 3 cms long and 1 cm wide. Because of its smallness, I didn’t completely smooth it before putting it into polish, doing only one week in 400 grit before a pre-polish and pro-polish

Friday 21 May 2021: Three small tumble-polished stones from my first (and so far only) fossicking visit to Slope Point (southern-most piece of land of the South Island), collected in early March, finished polishing yesterday.

Stone One, about 2.5 cms.

Another side of Stone One.

Stone Two, 4 cms long.

Other side of Stone Two.

Stone Three, 3 cms.

This sign stands at the place that the tourists get directed to. Fossicking beaches are nearby but not easy to access.

Slope Point and adjacent beaches. Source: Google Maps.

The next Post in this Series is here.

FB Group Posts: 15, 16 & 17 May 2021 – Birdlings Flat “Polish Failure”, Another Birdlings Flat Quartzite, and Birdlings Flat Banded Agate

This is the fifth in this Series reproducing my recent regular Posts in the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils”. The first Post in this Series is here.

Saturday 15 May 2021: The failure to polish… There are two processes I enjoy – finding interesting stones, and seeing them tumble-polished. The first does not always lead to the second – sometimes a stone does not polish, or not very well. After a few years’ experience, I have a good idea which stones will polish and which will not. Then there are those stones that look really interesting but I kinda guess they may not polish. Some I try anyway – because the stone is so interesting, and I have hope. I found this stone on Birdlings Flat on 24 August 2020 and finishing polishing it two days ago. It is 3.5 cms long.

One side of the polished stone.

Closer image of the polished stone.

Other side of the polished stone.

The stone as originally found on Birdlings Flat.

It didn’t really polish, but remains fascinating and will be kept in my collection. It is volcanic, [probably andesite], would originally have had lots of holes in it, and these holes have filled with minerals as water moved through over thousands and thousands of years. Generally, the infill material polished much better than the host material.

[Comments on this Post included “Some of the infill is banded and is tiny agates… Pretty red matrix too”, “Likely originated from the Rangitata River” and “See these in the Hinds River too. Varying sizes”.]

Sunday 16 May 2021: Birdlings Flat quartzite, recently tumble-polished, 5.5 cms long, still 3 or 4 very small areas of shallow rough places on it but I didn’t want to reduce it in size any more. It is far to interesting to me in its complexity to risk losing some of that by further tumbling.

Monday 17 May 2021: Banded beach agate, Birdlings Flat, just finished tumble-polishing. Five cms long, polished to a very smooth finish. I was amazed that the small marks caused by bashing against other stones and rocks in the waves actually seem to go quite deep, were not removed by tumbling (400 grit then polish).

One side of the polished stone.

Treasure

Held up to the sunny sky.

With a torch behind it.

The next Post in this Series is here.

Another South Island Fossicking Trip, February/ March 2021 – Days 19 and 20 (Kakanui, Moeraki Village, Katiki)

See here for the first Post in this Series.

Day 19, Sunday 7 March – Travel day. I drove north from Riverton to Kakanui (near Oamaru), and made a brief reconnaissance visit to Kakanui Beach (planning to spend two days here). I arrived at my favourite Kakanui Beach late afternoon and spent about 30 minutes checking out what stones were around. Here are five that I found:

This reasonably plain whitish quartz stone has this on its side.

Treasure

Limonite prase, a kind of jasper. This one has less holes than most.

Probably stained quartz.

Light coloured quartzite.

Plain beach agate, not a bad size.

Day 20, Monday 8 March – Kakanui, Moeraki Village and Katiki. To start off with today, I spent 3 1/2 hours on the beach near Kakanui.

The stones on the beach near Kakanui this morning.

You can see the wet strip of stones I followed today while fossicking. Looking south.

Looking northwards, towards Oamaru.

I went as far as these rocks, which are about 800 metres along the beach.

I found quite a few of the yellow and red quartzites that I like. I first came across a type of yellow quartzite at Birdlings Flat, near Christchurch, a few years ago and was pleased to discover even more of them appearing in the Kakanui area. Some have some red in them, and some I thought have almost no yellow (or red) at all. Here are 11 of these stones found today, starting with predominantly red ones, moving through to yellow ones then to increasingly plainer ones. Yet all the same type of quartzite, I reckon.

Among the other Kakanui stones I found today were these seven:

Fossil hash stone.

Not sure what might have caused these two flower-like-shapes, either fossils or some mineral process.

And these seven:

Nice sized quartzite.

Treasure

Small quartzite.

Jasper.

Another jasper.

In the afternoon I tracked back south for about 30 kilometres to visit a small beach not far from Moeraki village, a recommendation from Oliver who had earlier introduced me to Slope Point.

One end of the small beach near Moeraki Village.

Looking towards the other end of the beach.

Seagull on the small Moeraki Village beach.

There were seals at both ends of the beach so I did not venture further.

Oliver said I might find some agate there. And I did – botryoidal agate, seam agate, and sea-tumbled beach agate.

Botryoidal agate.

Seam agate, wet.

Beach agate, wet.

Other side of beach agate.

As noted by Jocelyn Thornton on page 11 of “Gemstones”, this form of cryptocrystalline silica is more accurately called “chalcedony”, with “agate” being used for the banded variety (see also Te Ara: The Encyclopedia of New Zealand). The Quartz Page provides a well-considered view on this. However, in New Zealand most varieties of chalcedony are often simply called agate. (Malcolm Luxton in “Agates of New Zealand” refers to some types of non-banded chalcedony as agate, such as those with mineral inclusions.)

Chalcedony is composed of very fine intergrowths of quartz and moganite. It is microcrystalline meaning the crystals are microscopic and cannot be observed by the naked eye. Both quartz and moganite have the same chemical formula SiO2 (silicon dioxide) but different crystal structures. When free from impurities, chalcedony is colourless and transparent. Dependent on impurities introduced during its formation, chalcedony comes in a wide variety of colours including red, yellow, green, blue, purple, grey, and white.

I was astounded to find the piece of botryoidal chalcedony/agate, having never come across it before. It was partly buried in the sand and I missed it first time I walked past. I went back a few paces for some reason to look at something else and noticed it from that direction.

One of the other sides of the botryoidal chalcedony.

Another side of the botryoidal chalcedony.

Held up to the sun.

As one website puts it, “Botryoidal minerals form when many nearby nuclei, specks of sand, dust, or other particles, are present. Acicular or fibrous crystals grow radially around the nuclei at the same rate, appearing as spheres. Eventually, these spheres abut or overlap with those that are nearby.” The Moeraki/Kakanui area is well known to have agate/chalcedony, as indicated on the map of rock collecting sites in Te Ara (see photo on left below). The Otago Rock and Mineral Club have a photo of a botryoidal chalcedony with a movable cap from the Moeraki area and a piece from Moeraki sold last year from the Trevor Gray collection (photos centre and right below).

Source: https://teara.govt.nz/en/map/5113/rock-collecting-sites-in-new-zealand

Source: https://sites.google.com/site/theotagorockandmineralclub/photos-of-nz-rocks-minerals-and-fossils-1

Moeraki area botryoidal chalcedony. Source: https://www.facebook.com/TheFamilyJewelsDunedin/posts/154609632961753

Seam chalcedony or agate is a form of this type of rock where layers build up to fill cracks and cavities in sediments (instead of occurring in holes left by gas bubbles in volcanic rocks). Jocelyn Thornton’s “Gemstones” includes an example on page 11. Craig McGregor has an interest in a particular type of seam agate found on the beaches on the south side of the Moeraki Peninsula. He calls it “Tobacco Agate” because of its very streaky layering. Again, I was astounded to find a good-sized piece of seam agate high up the beach, with very few other stones around it.

“Top” of seam chalcedony, dry.

Seam chalcedony held up to sun.

“Bottom” of seam chalcedony, dry.

“Top” of seam chalcedony, dry.

“Side” of seam chalcedony, wet.

The sea-tumbled beach chalcedony/agate I found might have started off as a seam but through wave action, being rolled against sand and other stones, it became shaped into a rounder form. You can often see tiny “concussion” marks on the surface of beach chalcedony, caused by being slammed into rocks and stones by waves and/or the current. Such marks are most noticeable when the stone is dry.

The beach-tumbled chalcedony I found, dry.

Concussion marks.

After my visit to this small beach near Moeraki Village, I went south another few kilometres to the Katiki Beach North Reserve Rest Stop. I had noticed some stones on the beach there yesterday when driving past. A scattering of stones was to be seen across pa lot of the beach. A 20 minutes fossick turned up a handful of interesting stones, and the potential existed for more, but the afternoon was wearing on and I headed back north to Kakanui and my accommodation.

Katiki Beach, looking north.

Katiki Beach, looking south.

The scatter of stones on Katiki Beach.

Stones on Katiki Beach.

Katiki beach stone.

Katiki beach stone.

Katiki beach stone.

The next Post in this Series, on Days 21 and 22, is here.

Stay-at-Home Day Twenty-Six, Monday 20 April 2020: Stone Twenty-Six

Stone Twenty-Four.

Stone Twenty-Three.

Stone Twenty-Two.

Stone Twenty-One.

Stone Twenty-Six is a polished banded agate stone from Birdlings Flat. I found it over a year ago and, after it had been stored for a few months, finished polishing it last month. It carries scratches and other damage from being smashed against rocks and stones by powerful waves. In order to keep the stone at a decent size, all of the bumps and nicks have not been smoothed away in the tumbler.

Stone Twenty-Six.

Other side of Stone Twenty-Six.

The bands become clearer when the stone is viewed edge-on, and when it is held up to light.

Edge view of Stone Twenty-Six.

Held up to the light (inside), edge view of Stone Twenty-Six.

Just as hydrogrossular garnets are the most sought-after stones on Gemstone Beach, so agates are the most sought-after stones on Birdlings Flat.

Stone Twenty-Six up close.

Stone Twenty-Six up close. The small cresent shapes are probably the result of percussive blows from other stones.

Stone Twenty-Six up close.

Agate is a cryptocystalline form of quartz that has precipitated from silica-bearing groundwater in rock cracks and cavities. It is similar to the way “sinter” is preciptated from geothermal hot waters flowing from geysers and hot springs. We are more used to agates as polished slabs of colourful semi-concentric patterns, the colour caused by various minerals like iron and manganese. Malcolm Luxton has published an amazing book, “Agates of New Zealand” (2015), which is packed full of information on and photos of such agates as found in New Zealand (available from the likes of Wheelers).

From Malcolm Luxton’s “Agates of NZ” (2015), p. 91.

From Malcolm Luxton’s “Agates of NZ” (2015), p. 192.

From Malcolm Luxton’s “Agates of NZ” (2015), p. 254.

From Malcolm Luxton’s “Agates of NZ” (2015), p. 144.

From Malcolm Luxton’s “Agates of NZ” (2015), p. 230.

Luxton notes that much agate material is discharged by Canterbury rivers into the sea and some of it is cast back onto more than 100 kilometres of Canterbury beaches. The movement of agates by northerly coastal currents “accounts for the notoriety of Birdlings Flat as an agate-collecting destination” (Luxton, 2015, page 250). Vince Burke’s Birdlings Flat Gemstone and Fossil Museum contains a number of magnificent agate slabs from especially Canterbury. And the Museum also contains many specimens of the smaller plainer agates to be found at Birdlings Flat.

Colourful agate slabs, Birdlings Flat Gemstone and Fossil Museum.

Agate stones, Birdlings Flat Gemstone and Fossil Museum.

Colourful agate slabs, Birdlings Flat Gemstone and Fossil Museum.

Agate stones, Birdlings Flat Gemstone and Fossil Museum.

These small agate stones, like Stone Twenty-Six, are the remnants of the breaking up of the colourful slab agates, coming from the un-coloured surrounding rock. They are often very plain and only sometimes have bands (layered precipitated material).

Holding Stone Twenty-Six up to the light, it is possible to see that agate is much more translucent than hydrogrossular.

Stone Twenty-Six held up to the light, outside.

Stone Twenty-Six held up to the light, inside.

And the patterns revealed in the light, from the history of the stone’s formation and battering by the waves against other stones, are utterly fascinating.

Stone Twenty-Six.

Stone Twenty-Six held up to the light – detail, with colour saturation.

Stone Twenty-Six held up to the light – detail.

The next Post in this Series is Stay-at-Home Day Twenty-Seven, Tuesday 21 April 2020: Stone Twenty-Seven. The first Post is Stay-at-Home Day One, Thursday 26 March 2020: Stone One.

Birdlings Flat Stone Collection Trip, February 2020

I spent five days based in Christchurch in late February, which enabled me to visit Birdlings Flat beach four times. The sea was very calm over this time and the weather posed no difficulties. At times, I was the only one on the beach or there were only two or three others there, walking a dog or fishing or also looking for interesting stones.

Clouds over Banks Peninsula, viewed from Birdlings Flat.

Birdlings Flat on a calm day.

Birdlings Flat, 24 February 2020.

A dog walker in the faraway. Birdlings Flat, 21 February 2020.

Three seagulls, Birdlings Flat, 21 February 2020.

Driftwood construction, Birdlings Flat, February 2020.

Looking through a driftwood construction, Birdlings Flat, February 2020.

On one of the days, during a weekend, a group of photographers were at the Banks Peninsula end of the beach, making the most of the cliffs, waves and sky. I was accompanied that day by Diane, my niece and host. As we neared the photographers, we came across an unusual creature on the stones – it looked kind of like a sea caterpillar, but I have not been able to identify it.

Unidentified beach creature.

Photographers, Birdlings Flat.

Unidentified beach creature.

I collected just over 9 kilograms of stones to take home to polish. I found a few beach agates, one of which had some very nice bands. I also saw some of my favourite yellow quartzite stones, including a couple of larger ones that had to be left on the beach.

An excellent banded agate found on Birdlings Flat, 24 February 2020.

The banded agate in amongst the stones on Birdlings Flat.

A different agate collected on Birdlings Flat, February 2020.

Large yellow quartzite stone, Birdlings Flat, February 2020.

In between visits to Birdlings Flat, Diane and I drove an hour inland and took a jet boat trip up the gorge of the Waimakariri River. We were fortunate enough to be the only two customers for Alpine Jet Thrills for that trip and had two guides to show us the landscape features. The geology of the gorge was interesting, though the rocks swept down the river to the sea end up north of Banks Peninsula and would not make their way to Birdlings Flat.

Diane (right) and our two guides/drivers from Alpine Jet Thrills, Waimakariri River.

On the Waimakariri River.

Geological formations of the Waimakariri River gorge.

Another Visit to Birdlings Flat, Late June 2016 – Part Three: Seven Types of Stones Collected

During the six to seven hours spent at Birdlings Flat and nearby beaches during two and a half days at the end of June, I collected just over eight kilograms of stones. These consisted of a number of different types of stones. After my two previous visits, I had a good idea of what I was looking for, based on the results of some tumble polishing as well as my own preferences. There are many greywacke stones on the beach, the common grey beach stones of New Zealand, as well as a wide range of other types.

Following are listed the seven types of stones I collected during this visit:

Yellow-patterned Quartzite; Red Jasper; Agates; Green (Quartzite?); Patterned; White Quartz and Other Light-Coloured; Others.

Yellow-patterned Quartzite – This can easily be found at Birdlings Flat and is perhaps my favourite stone from there. I discovered a small boulder of it, that filled both my hands – which I had to leave at the beach. I have brought home at least two hand-sized specimens. There are a number of subtle colour variations of this stone, the best seeming to be a clear to light coloured quartzite with curtains or swirls of “gold foil” throughout it. The intensity of the gold/yellow can vary from stone to stone as can the patterns inside it. During this trip, I sought to collect stones exhibiting these variations.

Dry stones, as collected in late June

The same stones, wet

An idea of size

Collected earlier, smaller and with brighter yellow through it

Collected earlier

Collected previously from Birdlings Flat – swirls of gold through the clear silica

Collected earlier

Red Jasper – Red jasper stones can often be found on South Island beaches. They are reasonably easy to find at Birdlings Flat, where they can be of good size and quality. Many jasper stones have silica veins, sometimes bright red veins as well, and some other mineral staining can be present. They can be brittle, with chips and pits, making them difficult to smooth and polish.

Dry stones, probably jasper, collected from Birdlings Flat in late June

The same stones, wet

Collected at Birdlings Flat at an earlier date

Collected earlier

Agates – Birdlings Flat is well-known for its agates. A wide range of sizes, shapes and types can be found. It took me a while before I learned to spot them. The best way is to look towards the sun and your eye will be drawn to the light shining through them, even amidst a whole mass of other types of stones. On this trip, I found my largest agate so far, and a very small one with a green staining.

The agates collected at Birdlings Flat, late June, in their dry state

The same agates, wet

A sense of their size

Anagate collected at Birdlings Flat at an earlier date

Moss agate, from Birdlings Flat, collected earlier

Coloured agate, Birdlings Flat, collected earlier

Green (Quartzite?) – One of the interesting types of stones to be found at Birdlings Flat is green and I suspect is a type of quartzite. Again, there is a great diversity of them, from pale green through to lime green through to darker greens. I find them quite attractive and relatively easy to spot.

Dry green stones

The same green stones, wet

Patterned – I find myself drawn to even greywacke stones and other grey (or common coloured) stones if they have veins of white quartz through them or if they display layer patterns.

Dry

Wet

White Quartz and Other Light-Coloured – Going through the stones I collected, I find there are a number of white quartz stones and other white or light-coloured stones. These tend to catch my eye on any beach, standing out from the sand or the predominant grey of the most common stones on South Island beaches. I have learned to be more restrained in my collection of white quartz as it is easy to spot it and can soon mount up in the collection bag.

Dry

Wet

Others – What’s left in my collection bag after the rest have been taken away:

Pink stones are rare but present at Birdlings Flat. Some of these stones include ones of volcanic origin, characterised by small white pits

The same stones, wet

Dry, and…

…wet

Another Visit to Birdlings Flat, Late June 2016 – Part Two: Birdlings Flat Gemstone Museum Again

The second day of our visit to Birdlings Flat, Petra and I visited Vince and Colleen Burke’s Gemstone and Fossil Museum on Hillview Road. This time, Colleen opened up the Museum for us and we got to talk with her about Birdlings Flat and the stones in the collection. Vince then took over from her after about 15-20 minutes. Petra bought a good-sized batch of agatised wood which we will have a go at polishing sometime. Vince generously gave her three pieces of polished agatised wood, to give her an idea of the end product of polishing. Agatised wood is a form of petrified wood and is in effect a fossil. It forms when plant material is buried by sediment and thus protected from the decaying action of oxygen and organisms. Groundwater rich in dissolved solids flows through the sediment replacing the original plant material with minerals such as silica, calcite and pyrite or another inorganic material such as opal. The result is a fossil of the original woody material that often shows preserved details of the bark, wood and cellular structures. “Agatised” wood is wood that has been replaced by agate, a form of chalcedony or microcrystalline quartz.

After about 30 to 40 minutes at the Museum, we moved onto the beach and spent nearly three hours fossicking for stones, walking eastwards right up to the end of the beach where it butts up against Banks Peninsula. We collected a few kilograms of stones, and returned the next day to collect even more. The next post will look in more detail at the variety of these stones.