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Figure 1. Faceted Oregon sunstone crystals (2.75–7.71 ct) representing the variety of colors observed. Photo by Adriana Robinson. Courtesy of the GIA Museum. Gifts of Western Ventures (pear shape), Dust Devil Mining Co. (oval), and John and Laura Ramsey (emerald cut on the far right).

Special Colors and Optical Effects of Oregon Sunstone: Absorption, Scattering, Pleochroism, and Color Zoning

Shiyun Jin, Aaron C. Palke, Nathan D. Renfro, and Ziyin Sun, November 3, 2023

Details the colors and optical effects caused by metallic copper inclusions in this gem-quality feldspar.

The Cause of Iridescence in Rainbow Andradite from Nara, Japan

Thomas Hainschwang and Franck Notari, December 11, 2006

“Rainbow” andradite from Nara, Japan, occurs as relatively small orangy brown crystals that show attractive iridescence in almost the entire range of the spectrum.

Buff-Top Round Diamond

Siau Fung Yeung, March 29, 2013

The New York lab recently examined several diamonds with an interesting variation on the cabochon.

Iridescence in iris quartz from Jalgaon, India

Causes of Iridescence in Natural Quartz

Xiayang Lin and Peter J. Heaney, May 8, 2017

Describes the occurrence of iridescence, and the role of differential etching, in quartz crystals from India’s Jalgaon District.

Evidence of Rotation in Flame-Structure Pearls from Bivalves of the Tridacnidae Family

Jean-Pierre Gauthier, Jacques Fereire, and Thanh Nhan Bui, August 15, 2019

A study of these pearls to characterize their distinctive flame structure and examine the possibility of rotation during their formation or growth.

Figure 1. A hackmanite with a faded purple color after storage in the dark (left), illuminated with long-wave UV light (center), and after removal from a few seconds of exposure to the long-wave UV light (right). The color has deepened after exposure to UV light. Photos by Ronnakorn Manorotkul.

Apatite in Hackmanite

E. Billie Hughes, May 23, 2023

A dramatic color change is observed in a hackmanite sample with an apatite inclusion.

Figure 1. Faceted and rough synthetic wakefieldite in LED lighting with 6400K color temperature. The faceted stone is 5.04 ct. Photo by Adriana Gudino; courtesy of Arya Akhavan.

Synthetic Color-Change Wakefieldite

Ziyin Sun, Shiyun Jin, Adriana Gudino, Aaron C. Palke, and Arya A. Akhavan, May 23, 2023

A report on the striking color-change behavior of the first faceted synthetic wakefieldite seen at GIA.

Figure 1. The Heart of Australia, a 3,510 ct double pseudomorph ikaite-calcite-opal gem specimen, is considered one of the finest ever unearthed. Courtesy of Graeme Dowton.

Rare Double Pseudomorph Ikaite-Calcite-Opal

Si Athena Chen and Jennifer Stone-Sundberg, May 23, 2023

One of the finest specimens of double pseudomorph ikaite-calcite-opal ever unearthed was on display at the Pueblo Gem & Mineral Show.

Figure 1. These two quartz crystal scepters containing a multitude of complex petroleum fluid inclusions (left) that fluoresce yellow to blue to long-wave UV light (right) are from a new deposit in Madagascar. The larger crystal weighs 11.05 ct and measures 22.81 mm in length. Photos by Annie Haynes; courtesy of Hidden Gem Gallery.

New Find of Petroleum-Included Quartz from Madagascar

Nathan Renfro and John I. Koivula, May 23, 2023

Examination of quartz from a new source in Madagascar reveals complex fluid inclusions consisting of petroleum, methane, asphaltite, and water.

Figure 1. Top: A series of images showing the gradual change (left to right) in the phosphorescence of the 0.71 ct HPHT-grown colorless diamond after removing it from the LWUV source (left image) in increments of 30 seconds for 150 seconds (right image). Bottom: The gradual change in phosphorescence after exposure to a SWUV source (left image) in increments of 30 seconds. The greenish blue and orange emissions decay differently, with the blue fading faster (~90 seconds, fourth image from left) than the orange (~240 seconds, right image). Images by Guy Borenstein.

HPHT-Grown Colorless Diamond Displaying Unusual Phosphorescence Effects

Guy Borenstein and Sean O’Neal, May 23, 2023

Study of phosphorescence produced from visible light suggests future difficulty in accurately assessing bodycolor of HPHT-grown diamonds.

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