GEM KNOWLEDGE · LABORATORY NOTES
Microcline Perthite
Sold as “Red Amazonite,” this specimen tested as microcline perthite. The report recommends the name perthitic microcline.
Sample: 10612 (‘red amazonite’). Header date: July 2, 2024. Signature date: July 21, 2024.
Finding: Bulk microcline with exsolution lamellae of albite.
Perthitic microcline rather than red amazonite
The report identifies the characteristic intergrowth of potassium feldspar (microcline) and albite. It recommends “perthitic microcline,” rather than “red amazonite.”
Amazonite is the green-to-blue-green variety of pegmatitic microcline. The report explains that lead and structural water are both involved in developing that color. This specimen contains approximately 400 ppm lead, but lead alone does not make a non-green microcline amazonite.
Also listed as: Red Amazonite · Microcline Perthite.
View the original test results
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These results are the property of Soul Body Gems, Alexander Falster, and the Maine Mineral & Gem Museum. Any mention requires full acknowledgment.
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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Electron microscope image: This view shows small-scale regions selected for analysis. Its brightness contrast helps distinguish regions with different compositions; it is not a photograph of their natural colors. Numbered spots connect this view to the analyses listed in the report.
Laboratory figure caption: Fig. 2: Backscattered electron image of an area of one of the broken beads.
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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. 3: Energy dispersive spectrum of spot 1 in Fig. 2. (potassium feldspar, microcline)
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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. 3: Energy dispersive spectrum of spot 2 in Fig. 2. (albite)
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Element map: This map shows where the named elements occur within the analyzed area. Its colors represent the laboratory’s selected element channels, rather than the specimen’s visible colors. The caption below preserves any color key or distribution noted by the laboratory.
Laboratory figure caption: Fig. 4: X-ray maps of the area shown in Fig. 2. potassium: purple, sodium: golden.
Read the report as text
Analytical Result Report Sample id: 10612 (‘red amazonite’) Submitted by: Soul Body Gems Date completed: 7-2-2024 Operating conditions: An AMRAY 1830 SEM operated at 25 kV acceleration potential, 24 mm working distance, 0 degrees sample tilt, coated with 250 Å carbon, and also using the attached XRF unit operated at 30 kV. Fig. 1: Photograph of the specimen. 60 mm diameter. Fig. 2: Backscattered electron image of an area of one of the broken beads. Fig. 3: Energy dispersive spectrum of spot 1 in Fig. 2. (potassium feldspar, microcline) Fig. 3: Energy dispersive spectrum of spot 2 in Fig. 2. (albite) Fig. 4: X-ray maps of the area shown in Fig. 2. potassium: purple, sodium: golden. Summary of findings: This specimen (Fig. 1) is a typical microcline perthite. Microcline is the bulk (Figs. 2 and 3) with exsolution lamellae of albite (Figs. 2 and 4). This is typical for plutonic potassium feldspars, especially in pegmatites. This should be called perthitic microcline and not red amazonite. Amazonite is the green to blue-green variant of pegmatitic microcline that owes its color to the effects of lead and water. Many non-green/green-blue microclines have quantifiable lead but the corresponding amount of structural water is also needed for green to blue-green color to develop. Incidentally, this specimen does contain about 400 ppm lead. Date: July 21, 2024. Signature. Transcription note: The duplicate Figure 3 numbering and differing header and signature dates are retained from the report.
Further reading: what gives amazonite its color?
A 2004 research abstract in Rocks & Minerals, “The Cooperative Effects of Lead and Structural Water on Color Intensity of Microcline, Var. Amazonite,” by P. E. Rein, W. B. Simmons, A. U. Falster, M. A. Wise, and J. W. Nizamoff, investigates why lead content alone does not explain amazonite’s green-to-blue color. The authors examined microcline from nineteen localities and considered structural water alongside trace elements. Their discussion also connects color development with radiation-related changes in lead.
Why this matters here: Detecting lead in feldspar does not, by itself, establish that it is amazonite. This research provides background for the distinction between green-to-blue amazonite and the perthitic microcline sold as “Red Amazonite.” It is supporting literature, not an additional test of our specimen.
Reference: Rein and colleagues (2004), Rocks & Minerals, September/October, pp. 342–343.