TumbleStone Calendar 2026: February – Banded Argillite

The Introduction to this Calendar can be found here. The Calendar features groups of beach stones I have collected recently, a different group each month. The stones are rough (un-polished) and usually wet, showing their colours and details. These 2026 Calendars are for sale, with postage within New Zealand included, for $35 non-rural, $40 rural. Two Calendars to the same address cost $60 non-rural, $65 rural. Three Calendars to the same address cost $85 non-rural, $90 rural. Email me at john.tumblestone@gmail.com.

The month of February features five banded argillite stones, four from Gemstone Beach and one (Stone Three) from Papatotara, a few kilometres further west. Argillite is a hardened mudstone – more details can be found in “M is for Mudstone from McCracken’s Rest”. Layers or bands of differently hued sediments are preserved in these stones. Generally, banded argillites come in green, gray, or brown, often with very dark or very light bands as well. Sometimes the bands seem to have a pottery glaze appearance, maybe due to extra time under heat and pressure.

Stone One (top row, left, in the Calendar) is a good example of maybe the most attractive form of banded argillite, with its semi-regular light and dark bands :

It is a small stone, found on Gemstone Beach on 23 August 2025, but I have found larger ones very similar in character, such as the one in “B is for Banded Argillite”.

In Stone Two a couple of the bands seem to have mixed, the band boundary having partially broken down. Maybe this happened when currents on the ocean floor, or a passing fish, disturbed the sediments. Stone Two was found on Gemstone Beach in March 2024:

Stone Three has a similar disturbed band boundary as Stone Two:

It was found on 15 August 2025 at Papatotara, about 15 kilometres west of Gemstone Beach along the Te Waewae Bay coast. A week earlier, I had picked up Stone Four on Gemstone Beach:

Stone Five looks as if it has been affected by tectonic stress, with some of the bands broken up and dislodged:

It is also a Gemstone Beach find, from early March 2025. Because of their original neat and regular banding, banded argillites provide very good displays of the effects of tectonic stress.

For March’s stones, see this Post.