Gem Profile- Cryptocrystalline Quartz Introduction

by Judy Ellis

As you have become aware in recent months, there are many, many kinds of quartz dug from the earth's surface! However, it wasn't until the 1800s that the many kinds were recognized as all having the same substance, SiO2, making them all quartz. This was discovered by the Swedish chemists Bergmann and J. J. Berzelius.

Quartz categorizes into three types in the old system.

Macrocrystalline quartz forms visible crystals like citrine, amethyst, and smoky quartz.

Microcrystalline quartz (agates) shows tiny grains under microscope.

Cryptocrystalline quartz (carnelian, chrysocolla) packs so densely crystals evade microscopes.

Modern usage calls macrocrystalline "quartz," cryptocrystalline "chalcedony."

Jasper falls under chalcedony; Dale detailed jaspers in Gem Profiles starting here.

Agate spheres photographed from Granite Mountain Nature Gallery's booth at Ogden gem show.

How are Macro- and Cryptocrystalline Quartz Different?

Macrocrystalline quartz differs from crypto- and microcrystalline forms in appearance and structure.

Macrocrystalline types like amethyst and rose quartz appear transparent-translucent, while agates (microcrystalline) and cryptocrystallines are often opaque.

Cryptocrystallines show softer hardness (6.5 Mohs vs. 7), duller wax-like luster, higher water content, and up to 20% non-quartz minerals-often deeming them "rocks" rather than pure "gems."

Macrocrystalline quartz grows by layering molecules outward into surroundings; cryptocrystalline forms from silica-water solutions molded precisely.

Silver Leaf Agate and Tree Agate cabochons exemplify these traits.

Types of Chalcedony (Cryptocrystalline)

Chalcedony varieties besides agate include carnelian, chrysoprase, onyx, thundereggs, petrified wood, and sometimes aventurine.

Found worldwide, including all 50 U.S. states, chalcedony dates to the Bronze Age.

Used in Mediterranean jewelry, beads, and wax seals wax wouldn't stick.

Name derives from ancient Greek village Chalkedon, now Istanbul.

Idar-Oberstein, Germany, gained fame in the 19th century for processing, dyeing, and preparing chalcedony and agate for carving and jewelry.

Many chalcedonies, especially agate, dye well; some like carnelian undergo heat treatment for deeper color.

Agate is a chalcedony quartz variety known for fine banding and bright colors.

Composed of about 90% quartz and 10% impurities plus moganite (another SiO₂ form).

Linked to volcanic activity, found in metamorphic rocks, veins, lava cavities, or even dinosaur bones.

Used in jewelry and carvings for millennia, discovered along Sicily's Achates River over 3,000 years ago.

Often forms druzy quartz or amethyst crystals if cavities remain unfilled.

Varieties include fire agate, tree/moss agate, plume agate, and geodes.

Druzies fill this agate cabochon.

Gem Profile- Cryptocrystalline Quartz Introduction

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