GEM KNOWLEDGE · LABORATORY NOTES
Zebra Stone from Australia
A banded cabochon from Western Australia, examined to understand its dark stripes and pale matrix.
Tested specimen: 9192 · Report completed: September 15, 2020
Key finding: The darker bands are rich in iron oxides, mainly hematite. The finer matrix consists of quartz and clay minerals. Iron was much more concentrated in the dark area than in the tan area.
What the report means
The report places the material near Kununurra in Western Australia and describes it as late Precambrian, around 600 million years old. A microbial contribution to the banding is presented as a possibility, not a demonstrated conclusion.
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Mineral identification is specific to the sample analyzed. The full report pages preserve the laboratory's wording and limitations.
Understanding the report figures
Use this guide alongside the written findings and the original report transcript. It explains the purpose of each analytical figure and preserves the laboratory’s own figure labels. The interpretations apply to the tested specimen; signals alone do not establish the identity of every similar-looking stone.
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Elemental spectrum: The peaks record characteristic X-ray signals from elements in the analyzed spot or area. This is an analysis of that location, not automatically of the entire specimen. Any mineral identification or uncertainty named in the laboratory caption is retained below.
Laboratory figure caption: Fig. 2: Energy dispersive spectral analysis of the dark brown area in Fig. 1.
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Elemental spectrum: The peaks record characteristic X-ray signals from elements in the analyzed spot or area. This is an analysis of that location, not automatically of the entire specimen. Any mineral identification or uncertainty named in the laboratory caption is retained below.
Laboratory figure caption: Fig. 2: Energy dispersive spectral analysis of the tan area in Fig. 1.
Read the report as text
This transcription makes the laboratory findings, figure captions, and table values available without opening the page images. Refer to the original images above for visual details.
Laboratory report
Analytical Result Report Sample id: 9192 (Zebra stone) Submitted by: K.Bitner Date submitted: Sept. 9, 2020 Date completed: Sept. 15, 2020 Operating conditions: JEOL JSM-6400 operated at 25 kV acceleration potential, 15 mm working distance, 15 degrees sample tilt, coated with 250 Å carbon. Using the X-ray fluorescence attachment with 35kv potental in conjunction with the EDS system. Fig. 1: Photograph of the Zebra stone cabochon. Maximum dimension is 28 mm Fig. 2: Energy dispersive spectral analysis of the dark brown area in Fig. 1. Fig. 2: Energy dispersive spectral analysis of the tan area in Fig. 1. element Dark brown area Tan area Iron 21.12 wt. % 2.33 wt. % Titanium 4700 ppm 2800 ppm Zirconium 244 ppm 237 ppm Phosphorus 340 ppm 350 ppm Calcium 120 ppm 6800 ppm Sulfur 2200 ppm 2000 ppm Summary of findings: This stone has a story! It comes from Western Australia near Kunnanurra. It is very late Precambrian in age, around 600 million years old. The darker bands are rich in iron oxides, mainly hematite. The matrix of the material is silty in grain size and finer and consists of quartz and clay minerals. Titanium, zirconium, and phosphorus and sulfur are present in both brown and tan areas, calcium is mainly present in the tan areas. This material may owe its striking colors to the action of life forms, microbes most likely. Bacterial mats may have precipitated the hematite, blue-green algae may have played a role in that. Interesting note, there is a location in Jackson County, Wisconsin, near Alma Center where a coarse sandstone is found which also has similar darker, iron-rich bands. That material is also Precambrian, possibly a little older, but it may have a similar origin. Locally, it is called ‘Zebra sandstone’. Date: September 15 ,2020 Signature
