Mai Zhiqiang
Red hair quartz, golden hair quartz, citrine, green phantom quartz, amethyst... The culture of crystals boasts a long and enduring history. With the progress of global trade, an increasing variety of splendid crystals are becoming a part of our lives. This article will guide you through an exploration of all things crystal-related.
1. Are crystals considered gemstones?
Crystals are single-crystal quartz minerals primarily composed of silicon dioxide. Quartz meeting gemstone-quality standards exhibits a brilliant glassy luster and high transparency. When containing various trace elements, it displays rich colors; when featuring unique inclusions, it demonstrates distinctive optical effects such as the cat's eye effect, star effect, and aventurine effect.
Crystal formation necessitates a conducive crystal growth environment, hydrothermal fluid rich in silica minerals, suitable high-temperature and high-pressure conditions, and prolonged time. Hence, crystals often form as clusters or geodes. Gem-quality crystal typically occurs in geodes or pegmatite veins, with vast distribution areas.
2. Types of quartz
(I) Gemstone quartz (single crystal)
Crystal (colorless), amethyst (purple), citrine (yellow-orange), green quartz (green), smoky quartz (brown), rose quartz (pink), as well as specialized bicolored crystals (such as ametrine), rutilated quartz, quartz cat's eye, starlight quartz, etc.
(II) Jade quartz (polycrystalline aggregate)
Chalcedony (yellow dragon jade, red chalcedony, green chalcedony, blue chalcedony, etc.), agate (nanhong, onyx, mossy agate, fire agate, etc.), quartzite jade (aventurine, etc.), jasper, silicified jade (tiger's eye, hawk's eye, petrified wood, etc.)
3. Differences between crystal glass and glass crystal
Beautiful crystals serve as inspirations for synthetic glass, both primarily composed of silicon dioxide. They share a similar crystal-clear appearance and are often indistinguishable at first glance. However, glass and crystal are entirely different in nature. Their divergent growth structures result in distinct properties when analyzed using gemological testing instruments.
Examine using a polariscope. Natural crystal exhibits four bright and four dark variations when rotated 360 degrees under a polariscope. At a specific angle, the distinctive "bull's eye" interference pattern of the crystal becomes visible, while glass remains completely dark or shows abnormal extinction behavior.
4. How is crystal classified and identified by the customs?
Upon receiving a crystal sample, the jewelry laboratory confirms its "identity" by weighing it, then examines its external characteristics and internal inclusions using a gem microscope. For identification purposes, instruments like refractometers, orthogonal polariscopes, and infrared spectrometers are utilized. A comprehensive analysis is performed based on data from close inspection and instrument measurements, resulting in an accurate product classification. The natural crystal is classified under tariff line 7103.9920. Its processing status is categorized as unprocessed, involving simple procedures such as sawing, rough forming, drilling, grinding, heat treatment, and filling. The product is neither in a string nor mounted. For items composed of natural crystal that exclude precious metals, the applicable tariff line is 7116.2000.
5. Customs reminder
(I) When purchasing crystal jewelry, consumers should pay attention to whether the crystal has been subjected to dyeing, filling, or coating treatments. Synthetic crystals are relatively common in the market and are difficult to identify through conventional testing methods. Accurate identification requires a professional gemology laboratory.
(II) Crystals possess stable properties and high hardness, making them suitable for safe daily wear. However, for certain varieties such as rose quartz, amethyst, and dyed agate, it should be noted that prolonged exposure to strong light and high temperatures may result in fading. Exercise caution when using ultrasonic cleaners to clean crystal jewelry.
(III) Crystal jewelry or items carried or shipped internationally by individuals should be for personal use, within reasonable quantities, and subject to customs supervision. Owners of items for import or export must truthfully declare them to customs and accept customs inspection.
(Author Affiliation: Huangpu Customs)
Disclaimer：The above content is translated from Chinese version of China Inspection and Quarantine Times. The China Inspection and Quarantine Times version shall prevail.
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