Black Agate Tumblestone Natural Polished Chalcedony Quartz Crystal 15-30mm Genuine Collector Stone with Certificate

Black Agate Tumblestone – Natural Polished Chalcedony Quartz

This genuine Black Agate tumblestone is a carefully polished variety of chalcedony, belonging to the quartz mineral family. Selected for its smooth finish, deep colour, and balanced shape, each piece measures approximately 15–30mm. The photograph shows an example of the actual specimen you will receive. Please refer to the listing images for full sizing and natural variation within this range.

Your Black Agate tumblestone includes a Certificate of Authenticity lifetime guarantee generic card, confirming it is a genuine mineral specimen.

Mineral Species & Classification

Black Agate is a variety of chalcedony, which itself is a microcrystalline form of silicon dioxide (SiO₂). It belongs to the quartz mineral group and forms within the trigonal crystal system, although its crystals are too fine to be seen with the naked eye.

Key mineralogical properties include:

• Mineral Group: Quartz (Chalcedony variety)

• Chemical Formula: SiO₂

• Crystal System: Trigonal (microcrystalline structure)

• Hardness: 6.5–7 on the Mohs scale

• Lustre: Waxy to vitreous

• Transparency: Opaque to slightly translucent at edges

• Fracture: Conchoidal

Agate forms in concentric bands within volcanic rock cavities, where silica-rich solutions deposit layer upon layer over time.

Colour & Surface Characteristics

Black Agate is known for its rich, deep black to charcoal tone. Depending on the specimen, you may observe:

• Uniform black colouring

• Subtle banding patterns

• Slight translucency along thin edges

• Smooth, high-gloss polished surface

The tumbling process enhances the stone’s natural texture, creating a rounded, tactile finish while preserving its mineral integrity. The 15–30mm size makes each piece easy to hold, display, or incorporate into a mineral collection.

Geological Formation

Agate forms in volcanic and igneous environments. When lava cools, gas bubbles create cavities within the rock. Over time, silica-rich groundwater enters these cavities and deposits microscopic layers of quartz, gradually building up banded chalcedony formations.

Black Agate may derive its dark tone from natural mineral inclusions such as iron or manganese compounds within the silica structure. It is commonly associated with:

• Basalt

• Quartz

• Calcite

• Other secondary silica minerals

The microcrystalline structure gives Agate its durability and smooth fracture characteristics.

Collecting & Display Appeal

Black Agate tumblestones are valued for their polished finish, durability, and classic appearance. The 15–30mm size makes them suitable for:

• Mineral cabinet collections

• Decorative bowl or tray displays

• Educational geology collections

• Collector gift pieces

• Craft or lapidary interest

Its deep, uniform tone offers a striking contrast when displayed alongside lighter quartz or banded agates. In some traditions, Black Agate is spiritually associated with grounding and balance; these associations are belief-based rather than scientific.

Authenticity & Careful Selection

Each Black Agate tumblestone is individually chosen for colour depth, polish quality, and overall presentation. The listing photograph shows an example of the actual specimen you will receive within the stated 15–30mm size range. Please review all images for scale and natural variation.

Every piece is supplied with a Certificate of Authenticity lifetime guarantee generic card, confirming its genuine quartz mineral origin.

A classic example of microcrystalline quartz formation, this Black Agate tumblestone offers smooth polish, durable structure, and timeless mineral appeal in a versatile display size.