February-March 2022 Fossicking Trip: Stone of the Day #15, Hydrogrossular Garnet from Gemstone Beach

My fossick today on Gemstone Beach resulted in many more hydrogrossular garnets being found than on any of my previous visits this month. I was on the beach at a higher tide level, starting just 90 minutes after high tide. This meant I was able to see many more wet stones than before because the waves were running higher up the beach – including more hydrogrossular garnets.

I have learned which stones are hydrogrossular garnets from talking to other fossickers I’ve met on Gemstone Beach over the past five years, from seeing specimens in museums and private collections, from members of Facebook Rockhound Groups, and from various published and online sources (e.g. page 9 of Jocelyn Thornton’s “Gemstones”). However, stone identification in general is often debatable (is a stone a jasper or a quartzite?) and even local knowledge can be fallible. This Post represents the current state of my knowledge of what is or is not a hydrogrossular garnet (or what stone may incorporate some hydrogrossular garnet within it).

This Post refers to ten hydrogrossular garnets, labeled from “a” to “j” so you can locate them in the following photo of most of the garnets I collected today. Hydrogrossular garnets come in a range of types and you can find them in various shapes and sizes:

Most of the hydrogrossular garnets I collected today, arranged by size. $2 and $1 coins for scale.

Stones a to j are included in this Post.

Today’s Stone of the Day is a small blue hydrogrossular garnet (labelled “a” above):

Stone #15.

This type is not translucent as many other types can be – I refer to it as a “porcelain-type” because of its cool feel and very fine structure. It stands in contrast to the likes of the next hydrogrossular garnet, one of the rich brown types (included below are photos with a torch behind the stone):

With a torch behind it.

A tumble polished brown hydrogrossular garnet similar to the one above features in this Post. The next four hydrogrossular garnets illustrate part of the range of types to be found on Gemstone Beach and further northwest along the shore of Te Waewae Bay:

The next four are either relatively translucent or too small for close-up photos to be very revealing:

It was cloudy for the first half of my fossick but the sun shone brightly during the second half.

Gemstone Beach stones.

A cloudy morning.

Paradise shelducks high atop the cliff at the back of Gemstone Beach.

Gemstone Beach stones.

The Taunoa Stream, not far from the carpark.

I also found a few other stones worth collecting:

Unusual colour trace fossils.

I suspect this is a trace fossil stone – it has bumps which could be the traces.

The first Post in this Series is here. The Index to all the Posts in the Series is here.