Four Polished Gemstone Beach Stones Gifted

Two recent overseas guests at our Air BnB in Whanganui showed a lot of interest in some of the stones I had collected and polished. A young couple, Omer and Elizabeth, booked in for one night and I greeted them and showed them where to go. I mentioned my hobby of tumble polishing beach stones and showed them a couple of colourful ones from a nearby garden (rejects from the tumbling process). This led to a walk over to my cluttered and untidy stone shed where I showed them my tumblers and some stones at various stages of processing.

Given their enthusiasm and appreciation, I decided to gift them four tumble polished stones from Gemstone Beach, three of which they had already seen and showed interest in, the fourth similar to some brecciated jasper that had also attacted their attention.

I had collected these four stones from Gemstone Beach, Southland, over the last couple of years. This beach is located 70 kilometres west of Invercargill, as described in this Post. I collect stones mainly from the beach in front of the carpark and further along to the Waimeamea River mouth – sections two and three in this Post.

A NOTE ON THE PHOTOS BELOW: Photos of stones often reveal a lot more than what can be seen when looking with the naked eye. There is much that is positive about this. Colours and patterns become more obvious, tiny details become visible. Close-up photos can show just how amazing an “ordinary” stone is. Stones One and Two below are good examples of this. There is also a negative side to the close-up photos of stones. They can reveal tiny scratches and imperfections in the polishing process, as well as less attractive aspects of a stone. Stone Three below has areas of white scratching which can lure your eye away from the amazing pink in it. Close-ups of Stone Four reveal how “dirty” some of its white crystals are. Generally, the positives well out-weigh the negatives – the photos allow you to explore a stone and appreciate it more more.

The first stone, Stone One, has really interesting circular features and patches of colour:

Some of the circles could be amygdaloidal in character. Amygdaloidal stones are also known locally as volcanic bubble-infilled stones. They originate in molten magma which may contain dissolved gas that forms bubbles in the rock as the pressure is released on eruption. These bubbles can get trapped in the solidifying rock, forming tiny holes called “vesicles”. These holes then fill with mineral-rich fluids which leave behind deposits of minerals such as quartz, chalcedony, calcite and zeolites. The resultant “spots” are called “amygdales” (also “amygdules”). This term comes from the Latin and Greek words for almond, reflecting the almond-shape of many such in-filled vesicles. However, amygdales can also be round and some can be irregular shapes. Many of the dark-coloured stones with amygdales on Gemstone Beach are basalt, as Stone One could be. For other examples, see “A is for Amygdaloidal” and “Stone of the Day #17, Small Gemstone Beach Amygdaloidal Stone”. Further Gemstone Beach amygdaloidal stones can be seen in this Post, Section 4, Stones W30 to W42.

Stone One also has interesting white, orange, yellow and green in it:

These are various minerals that are present in the stone, and their distribution and intensity would most likely have occurred as the rock was cooling. They have made some fascinating patterns, some circular. Sometimes the colour is inside an amygdale, sometimes in the basalt itself. The white could be quartz, the green is probably epidote, and the orange and yellow could be orthoclase feldspar and/or iron oxide.

Stone Two is a colourful jasper. Elizabeth had mentioned she hadn’t seen a stone of this colour before. We also talked a little about the poppy jaspers in the 2026 TumbleStone calendar, the month of April, and Stone Two has some poppy-like orbs visible on Side B:

Jasper is an opaque form of cryptocrystalline, or microcrystalline, quartz which is also known as chalcedony. It is formed from microscopic crystals of silica, often precipitated out of heated groundwater flowing through sedimentary rocks (GeologyScience). It is the presence of iron oxide that provides the red colour. In Stone Two, Side A has a real mix of patches of light and dark reds, white, orange, purple and yellow. Side B has some large orb-like structures, with maybe the hint of tiny red orbs in the lower left quadrant:

Orbs in jaspers form because minerals crystallise in concentric layers around a nucleus or central point. If the orbs are red or orange, they look like a field of poppies from above.

Pink was another colour that Omaer and Elizabeth admired in my stones. Stone Three has some lines of intense bright pink in it:

Pink is often due to the presence of manganese. The rare pink stones found on Gemstone Beach are sometimes thulite, the national gemstone of Norway where it was first identified – see “P is for Pink”, also the month of March in the 2026 TumbleStone calendar. I’m not totally certain that Stone Three is thulite but the way the pink is presented in it is consistent with thulite. The non-pink material in the stone could be plagioclase feldspar (a guess) – if it was quartz, it would have polished in a much cleaner and more shiny manner. In my experience, thulite often fails to polish well.

Two further close-ups of the pink in Stone Three, and then two photos (below, right) showing how the pink stones stand out on the beach when wet (Gemstone Beach, 25 February 2021):

Stone Four is striking because of its elongated white crystals against a dark background (found in September 2024):

The crystals are likely to be plagioclase feldspar and my guess is that the stone could be either gabbro or diorite, both igneous plutonic rocks. The different sizes and shapes of crystals in such stones depends on how quickly the molten rock has cooled and hardened, and what minerals are present to make up the crystals. A “volcanic” rock cools on the earth’s surface and, because it has solidified quickly, the crystals have not had time to grow very large. But for a “plutonic” rock, the molten rock has cooled much more slowly underground, giving the crystals time to grow larger, sometimes as large as fingernails. Similar Gemstone Beach stones with opaque white crystals can be seen in this Post, Section 5, Stones W43 to W63. The month of June in the 2026 TumbleStone calendar has photos of six igneous stones with white crystals of varying shapes and sizes – the Post about them has not yet been completed. Here are four of June’s stones:

THE PROCESS OF TUMBLE POLISHING – The aim of tumble polishing is to mimic the action of the sea’s waves by turning stones over and over, letting them bump into each other. Adding sharp silicon carbide grit (like the abrasive stuff on sand paper) hastens the smoothing process. This takes place in a rubber barrel (or similar), about two-thirds full of stones, water and grit. The barrel is rotated 24 hours a day for a number of days. Usually three or four different grades (sizes) of grit are used. Tumbling stones in a very coarse grit for seven to ten days removes maybe five to eight per cent from the surface of the stones. Finer grits are then used, again for seven to tens days at a time. These remove less of the stone but makes the surface very smooth, ready for a final polishing stage in a very fine polish powder such as tin oxide. Sometimes a stage needs to be repeated until a stone is smooth enough.

I collect smooth beach stones so I need to do less tumbling than people who find stones in streams or the ground. Most of my stones take between about 50 to 60 days to polish. More details can be found in “2) The Seven Stages in Tumble Polishing Stones” in this Post.