search
  • サインイン
    サインアップ
  • カスタマーサポートは英語のみでのご対応となります。

    Toll Free - USA & Canada only:
    1-800-464-1640

    国際電話:
    +66-39609697

  • 言語を変更する
  • USD

GemSelect December 2013 Newsletter: Amazing Gemstone Optical Phenomena

Phenomenal Gems - Optical Illusions of Colored Stones

Phenomenal gemstones which display unusual optical properties are extremely rare and quite unusual. Optical phenomena results from the way light interacts or interferes with the structural anatomy of a gemstone. The interaction or interference can be in the form of light scattering, reflection, refraction, diffraction, absorption or transmission. There are many forms of gemstone phenomena; some are quite common and rather simple and subtle, while others are considerably rare, incredibly striking and easily noticeable.

Light Beam Behavior
Light Beam Behavior

For many, the subject of gemstone optical phenomena can be very confusing not only with the how and why, but also with the terminology we use today to describe such optical effects. As most of us know far too well, understanding gemstone terminology is neither simple nor straight-forward, especially due to the fact that many gemological terms aren't even recognized by spellcheckers or even Merriam-Webster to say the least.

In our newsletter this month, we hope to help clarify and shed some light into the mystical world of gemstone phenomena and the confusing terminology we use today.

Adularescence Back to Top

Adularescence is an optical effect named after 'adularia', the historical name once used to refer to moonstone. The effect is owed to light interference caused by layered deposits of differing materials. The adularescence effect is often described as an internal surge of undulating light which appears to float about like a moveable cloud. The glow seems to originate from within the stone rather than the surface. Often times, the term 'sheen' is used to describe this effect, especially with rainbow moonstone.

Natural Moonstone from GemSelect
Moonstone Gem

Moonstone is by far the most famous for adularescence, but many other gems can exhibit this phenomenon as well, including opal; though opal adularescence is typically referred to as 'opalescence'. Less intense or 'mild adularescence' occurs more as a general scattering of light which results in a slightly hazy or milky appearance in otherwise non-hazy stones, very frequently seen in common opal and rose quartz.

Aventurescence Back to Top

The aventurescent effect is a sparkling or glittering effect caused by the reflection of light from tiny disc-like inclusions, typically composed of mica, copper or hematite. The terms 'schiller' or 'sheen' are very often used to describe aventurescence.

Obsidian Cabochon Gemstones
Obsidian Gemstones

Aventurine quartz is the best-known of aventurescent gems (and the reason why the phenomenon was named aventurescence). Even so, aventurescence can actually occur in a variety of other gemstones too, including various feldspars such as sunstone and andesine-labradorite. A variety of obsidian known in the trade as 'gold-sheen obsidian' is also known to exhibit an extremely attractive aventurescence.

Cat's Eye Chatoyancy Back to Top

Cat's eye chatoyancy is the unique reflection of light concentrated from parallel needle-like inclusions aligned within a single axis point. This results in a highly-focused band of light that appears as an 'eye' when a stone is properly oriented and cut en cabochon.

Natural Cat's Eye Gemstones
Cat's Eye Gemstones

Some especially high-quality cat's eye can exhibit a 'milk and honey' effect, which can be seen when moving a light to one side of the gem and concentrating it laterally; this results in one side appearing dark, while the other side appears light. Some rare specimens may also exhibit an ability to 'split eyes' when exposed to two different direct light sources. As the two lights shift angles, a single eye splits into two, each following one of the lights; this effect resembles an 'opening and closing eye' effect.

Chrysoberyl cat's eye is the most famous and original cat's eye gem, but this remarkable phenomenon can also occur with quartz, tourmaline, apatite, beryl and moonstone.

Simple Chatoyancy Back to Top
Pietersite gemstones
Pietersite Gemstones

Simple chatoyancy is also the result of parallel microscopic needle-like inclusions, but in the case of simple chatoyancy, the silky inclusions are not well-organized nor are they properly oriented to focus and concentrate the light into a single visible band. As a result, simple chatoyancy appears as multiple reflections of small silky and thread-like streaks of light. With only slight adjustments to its viewing angle, simple chatoyancy can cause a stone to change from light to dark and back to light again.

Tiger's eye, pietersite, seraphinite and charoite are the best-known gems that possess simple chatoyancy. Some very rare specimens of sapphire and ruby may also exhibit slight traces of simple chatoyancy which are caused by fine silk-like inclusions.

Asterism Chatoyancy Back to Top
Natural star gemstones
Natural Star Gemstones

The phenomenon of asterism (star) chatoyancy is technically just an expanded form of cat's eye chatoyancy. Like the cat's eye effect, asterism is also the result of parallel-aligned fibers and inclusions, but rather than aligning across a single axis point, they align along two or more axis points. The intersecting axis points with perfectly aligned inclusions results in a unique reflection of light in the form of a 4 or 6-rayed star.

Star specimens must be properly oriented and cut en cabochon with a high dome in order to maximize the desirable asterism. Star sapphire and star ruby are the most popular 'star gemstones', but there are actually many other star gems available, including star diopside, star garnet, star rose quartz and star moonstone.

Iridescence Back to Top
Iridescent gemstones
Iridescent Gemstones

Iridescence is a unique multicolor rainbow-like effect caused by light diffraction. As light passes through different layers of material with differing refractive indices, a prism effect causes light to separate into various spectral colors. Prismatic iridescent effects can also be caused by internal fractures and cleavage. Although iridescence is the most common optical phenomenon found in gemstones, it's also undoubtedly one of the most mesmerizing of effects.

Iridescence can be seen in many different types of gemstones, including fire agate, ammolite and rainbow pyrite. Perhaps the most well-known forms of iridescence are the 'play of color' seen in precious opal, and the delicate shifting in fine pearl, often referred to as 'the orient'.

Labradorescence Back to Top
Labradorite gemstones
Labradorite Gemstones

The labradorescent effect is caused by diffraction of light through fine platelets of differing compositions, as well as the presence of minute inclusions. The labradorescent effect is highly directional and produces stunning metallic spectral colors of bright blue, violet, green, red, orange and yellow-gold.

Labradorescence is a form of iridescence, but the term is only used when referring to labradorite gemstones owing to the uniqueness and intensity of this remarkable phenomenon. The labradorescent effect is sometimes referred to as a 'schiller' or 'sheen'. At some angles the schiller is completely invisible and dull, while other angles reveal an extremely vivid and absolutely remarkable schiller.

Pleochroism Back to Top
Sphene Gemstones
Sphene Gemstones

Pleochroism is the ability for gemstones to display different colors or depth of color when viewed from different angles. The phenomenon is caused by differing absorption of light rays in doubly refractive crystals. This means that singly refractive gemstones, such as spinel and diamond cannot exhibit any level of pleochroism. Dichroic (dichroism) is a term used to specify two color pleochroic gems (kunzite), while trichroic (trichroism) is often used to refer to gems that can display three colors (andalusite).

Pleochroic effects can be enhanced through specific orientation and in many cases, can be reduced or minimized through proper cutting as well. This is often done to show the more attractive of colors a gemstone may exhibit. Some of the most popular pleochroic gems include andalusite, iolite, kyanite, kunzite, sphene and tanzanite.

Color Change Back to Top

Color change is one of the rarer and more intriguing of gemstone optical phenomena. Unlike pleochroism, color change ability does not rely on viewing angle. With the color change phenomenon, colors can change when gems are viewed under different types of light such as daylight or incandescent light. Only rare gems which formed with multiple light transmission windows can exhibit the ability to color change (similar to the concept of doubly refractive crystals and pleochroism).

Natural Color-Change Gem
Natural Color-Change Gems

To help understand the phenomenon, a red gemstone appears red because it absorbs all frequencies of light except for red (one transmission window) - but a color change gemstone that absorbs all frequencies except for blue and red (two transmission windows) will appear blue when light is rich in blue wavelengths (fluorescent), and will appear red when the light is rich in red wavelengths (incandescent light). Although alexandrite is the best-known of color change gemstones (hence the term 'alexandrite effect'), the color change phenomenon can also occur in rare specimens of sapphire, garnet and diaspore-zultanite.

Tenebrescence Back to Top

Tenebrescence is the rarest of all optical phenomena. It is the unique ability for certain gemstones to change color when exposed to sunlight and for the process to reverse again once the light reverts. Another term for this phenomenon is 'reversible photochromism'.

Tenebrescence in Gems
Tenebrescence in Gems

Tenebrescence occurs in only a few minerals, one of which includes a rare variety of sodalite known as hackmanite. Hackmanite appears violet when it's first mined, but once exposed to sunlight, the color quickly fades to grayish or greenish white.  When placed back into a dark place for an extended period of time, the violet color slowly returns. The remarkable optical effect of tenebrescence can be repeated indefinitely and never fails to inspire awe in the viewer.

Phenomenal Gems make Phenomenal Holiday Gifts! Back to Top

Gemstones with optical phenomena are truly one-of-kind creations. They make excellent gifts for both novice and veteran gem collectors. Best of all, many phenomenal gems are surprisingly very affordable! We have a huge selection of pleochroic gemstones, gems with simple chatoyancy, cat's eye gems, star gemstones, gemstones with schiller and gemstones with sheen - and many are available for less than $25!

Click here to view thousands of gems from just $10 to $25!

Shipping Tips for the Holiday Season Back to Top

During the holiday season, courier services and post offices around the world are busier than ever. Although we will take special measures to ensure you receive orders promptly and reliably, there are still a few things you can do to help ensure your gems will be delivered on time. We strongly recommend opting for our express service shipping for all of your holiday gifts. It's fast! Typically, shipments arrive in just 3 to 4 days to nearly anywhere in the world. Also, if you require gemstone certification, please allow an additional 5 to 10 working days to complete the lab testing and certification (in addition to the transit time).

We hope you found this article interesting. If you have any comments or suggestions, just drop us a line. We really do read and reply to every single email we receive. Please make sure you can receive email from help@gemselect.com.

Lastly, we would like to wish you and all of your loved ones the best in health, wealth and success for the upcoming holidays as well the New Year!

Happy Holidays!
Your friends at GemSelect

  • 初刊: 12月-02-2013
  • 最終アップデート: 6月-22-2017
タッチで滞在
*GemSelectプロモーションメールを受信するためにサインアップしています.

プライバシーについて © 2005-2022 GemSelect.comは無断転載を禁じます。

GemSelect.com(SETT Company Ltd.)の書面による明示的な同意なしに複製(テキストまたはグラフィック)することは固く禁じられています。

2366

その他の形状
人気の宝石
  • サファイア
  • エメラルド
  • ルビー
  • アクアマリン
  • ジルコン
  • オパール
  • トパーズ
  • トルマリン
  • ガーネット
  • アメジスト
  • シトリン
  • タンザナイト
すべての宝石 (143)
  • アイオライト
  • アイドクレース
  • アクアマリン
  • アクチノライト キャッツアイ
  • アズライト
  • アパタイト
  • アベンチュリン
  • アマゾナイト
  • アメジスト
  • アメジストジオードスライス
  • アメトリン
  • アルマンディンガーネット
  • アンダルサイト
  • アンデシン ラブラドライト
  • アンモライト
  • インペリアルトパーズ
  • エメラルド
  • エンスタタイト
  • オニキス
  • オパール
  • オブシディアン
  • カイヤナイト
  • カラーチェンジする宝石
  • カラーチェンジガーネット
  • カラーチェンジサファイア
  • カラーチェンジダイアスポア
  • カラーチェンジフローライト
  • カルセドニー
  • カーネリアン
  • ガーネット
  • キャッツアイの宝石
  • キャッツアイアクアマリン
  • キャッツアイアパタイト
  • キャッツアイオパール
  • キャッツアイスキャポライト
  • キャッツアイムーンストーン
  • クォーツ
  • クォーツ キャッツアイ
  • クリソコラ
  • クリソプレーズ
  • クリソベリル
  • クロムディオプサイド
  • クロムトルマリン
  • クンザイト
  • グランディデライト
  • グロッシュラライト ガーネット
  • コーネルピン
  • ゴールドベリル
  • サファイア
  • サンゴ
  • サンストーン
  • サーペンティン
  • シトリン
  • シリマナイト
  • シリマナイトキャッツアイ
  • ジェダイト
  • ジェード
  • ジャスパー
  • ジルコン
  • スキャポライト
  • スコレサイト
  • スターガーネット
  • スターサファイア
  • スターストーン
  • スターディオプサイド
  • スタームーンストーン
  • スタールビー
  • スターローズクォーツ
  • ストロベチークォーツ
  • スノーフレーク・オブシディアン(黒曜石)
  • スピネル
  • スフェーン
  • スペクトロライト
  • スペサルティン ガーネット
  • スミソナイト
  • スモーキークォーツ
  • セラフィナイト
  • ソーダライト
  • タイガーズアイ
  • タイガーズアイマトリックス
  • タンザナイト
  • ターコイズ
  • ダイヤモンド
  • ダブレットオパール
  • チャロアイト
  • チョコレートオパール
  • ツァボライトガーネット
  • デマントイド ガーネット
  • デンドリティックアガート
  • トパーズ
  • トルマリン
  • ドゥルージー アズライト
  • ドルジーアメジスト
  • ドルジーバリサイト
  • ヌーマイト
  • ハイアライトオパール
  • ハウライト
  • バリサイト
  • パイライト
  • パイロープガーネット
  • パール
  • ピーターサイト
  • ファイアーアガート
  • ファイアーオパール
  • フローライト
  • ブラックオパール
  • ブラッドストーン
  • プレナイト
  • ヘソナイトガーネット
  • ヘマタイト
  • ヘミモルファイト
  • ヘミモルファイト ドゥルージー
  • ペリドット
  • ホークスアイ
  • ボルダーオパール
  • マウ・シット・シット
  • マザーオブパール
  • マトリックスオパール
  • マラカイト
  • マラヤガーネット
  • マリガーネット
  • ミスティックトパーズ
  • ムーンストーン
  • メノウ
  • メノウ ジオード
  • モルガナイト
  • ラピスラズリ
  • ラブラドライト
  • ラリマー
  • リソベリルキャッツアイ
  • ルチルクォーツ
  • ルビー
  • ルビーインフックサイト
  • ルビーゾイサイト
  • ルベライトトルマリン
  • レインボーパイライト
  • レインボームーンストーン
  • ローズクォーツ
  • ロードクロサイト
  • ロードライトガーネット
  • 化石サンゴ
  • 灰鉄輝石入りクォーツ
  • 白鉄鉱のクォーツ
主なカテゴリー
  • 新着商品
  • 宝石のまとめ買い
  • 標準サイズの宝石
  • 宝石
  • トップグレードの宝石
  • マッチするペア
  • カボション
  • 穴あき宝石、ブリオレット、ビーズ
  • 誕生石
  • 宝石の彫刻
  • ファンシー宝石
  • スターストーン
  • 熱処理なしのサファイア
カスタマーサポートは英語のみでのご対応となります。

Toll Free - USA & Canada only:
1-800-464-1640

国際電話:
+66-39609697

Save Money
No shipping Fees for Additional Items!
$8.90 Worldwide Shipping

Update Translation
 
Current Value
New Value
GemSelect Gemstones
X ウィンドウを閉じる
Colored Gemstones
X ウィンドウを閉じる
Colored Gemstones
X ウィンドウを閉じる
Colored Gemstones
サイズとウェイト

Gems are always measured in Millimeter (mm)

Dimensions are given as;
length x width x depth,
except for round stones which are;
diameter x depth

Select gems by size, not by weight!
Gem varieties vary in density, so carat weight is not a good indication of size

Note: 1ct = 0.2g

Size Comparison Chart