The Marvelous World of Calcite: Origins, Varieties, and Uses

Calcite is a versatile mineral treasured by lapidarists for its beautiful forms and dazzling colors. As a relatively soft mineral with a Mohs hardness of 3, calcite may not be suitable for all jewelry applications, but its variability makes it perfect for artful lapidary work. The most prized calcite specimens feature brilliant crystal formations, like the transparent Iceland spar renowned for its optical properties. Though too fragile for practical use, Iceland spar calcite exemplifies the mineral’s splendor.

Other common calcite varieties also attract lapidarists, including rhombohedral, prismatic, and stalactitic habits. Differently colored calcites like cobaltoan, manganoan, honey, and travertine showcase mesmerizing hues from pink to amber. Skilled lapidarists can shape these calcites into stunning cabochons or objets d’art. More durable limestone, composed largely of calcite, can be sensitively worked into remarkable lapidary pieces.

Calcite’s softness allows lapidarists to slice, carve, and polish the mineral into diverse designs. Coupled with its visual variety, these properties make calcite a favored material for artistic jewelry-making and ornamental lapidary work. Though delicate, calcite provides lapidarists with ample creativity and beauty. The mineral’s prevalence worldwide also ensures lapidarists can readily acquire superb specimens to transform into remarkable creations. For lapidarists, the splendor and workability of calcite is unparalleled among minerals.

What is Calcite?

Calcite is a carbonate mineral with the chemical formula CaCO3. It is the most stable polymorph of calcium carbonate, making up vast limestone deposits across the globe. As an abundant rock-forming mineral, calcite can be found in sedimentary, metamorphic, and igneous rocks worldwide. It makes up the shells of marine organisms, coral reefs, stalactites, and stalagmites.

Calcite has a defining property of effervescing or fizzing when exposed to hydrochloric acid. This reaction occurs due to the carbonate ions present in calcite. It also exhibits perfect cleavage in three directions due to its trigonal crystal structure. The cleavage planes of calcite allow it to break evenly along smooth planes, revealing its crystalline properties.

With a Mohs hardness of 3, calcite is relatively soft and can be scratched by a knife or copper coin. It has a vitreous to pearly luster and ranges from transparent to opaque. Calcite is doubly refractive and was used in Iceland spar for optical equipment due to its unique double refraction properties.

Calcite Crystal Habits

One of the features that makes calcite highly prized is its occurrence in over 800 crystal forms. Some of the main crystal habits include:

Rhombohedral Calcite

This classic habit exhibits a rhombic dodecahedron shape. The cleavage planes meet at obtuse angles, creating a diamond-like appearance.

Prismatic Calcite

Prismatic calcite crystals have a columnar structure and pointed terminations. They have a distinct prismatic cleavage and show oblique end faces.

Stalactitic Calcite

Stalactitic calcites are cave formations that hang from cave ceilings as icicle-shaped deposits. They form over long periods from dripping water rich in dissolved calcite.

Tabular Calcite

This habits forms tabular crystals with a square to rectangular shape. It is also known as nail-head calcite due to its resemblance to the head of a nail.

Scalenohedral Calcite

Scalenohedral calcites have a pyramidal shape with faces of unequal sizes and unequal angles between them, forming a scalene triangle.

Calcite Colors

Calcite occurs in every color of the rainbow based on the minerals present during its formation. Some of the most popular colored calcite varieties include:

Cobaltoan Calcite

Cobaltoan calcite acquires its distinctive pink to reddish hue from cobalt ions. The color varies based on the cobalt concentration.

Manganoan Calcite

This variety exhibits pink, red, or violet tones from traces of manganese. It is also referred to as manganocalcite.

Honey Calcite

As the name suggests, honey calcite has a warm golden brown or honey-like color. The yellowish tones result from hydrocarbons trapped during formation.

Iceland Spar Calcite

Iceland spar is renowned for its exceptional transparency and optical properties. It has a colorless to white appearance when pure, but also occurs in yellow, brown, green, and red hues.

Blue Calcite

Vivid blue calcite owes its color to arsenic or sulphur compounds. The blue can range from pale to a deep azure tone.

Orange Calcite

Calcite takes on orange colorations due to traces of phosphorus or manganese oxidizing over time. Orange calcite is also called sun or mango calcite.

Comparison of Calcite versus Other Rocks

Rock	Composition	Hardness	Density	Cleavage	Fracture	Uses
Calcite	Calcium carbonate (CaCO3)	3	2.71 g/cm3	Perfect in 3 directions	Conchoidal	Construction, lapidary, optical uses
Quartz	Silicon dioxide (SiO2)	7	2.65 g/cm3	None	Conchoidal	Gemstones, glassmaking, electronics
Feldspar	Aluminum silicates	6-6.5	2.55-2.76 g/cm3	2 directions at 90 degrees	Conchoidal	Ceramics, glassmaking
Olivine	Magnesium iron silicate	6.5-7	3.27-4.39 g/cm3	None	Conchoidal	Gemstones, refractory bricks
Obsidian	Silicon dioxide with impurities	5-5.5	2.35-2.8 g/cm3	Conchoidal	Conchoidal	Arrowheads, ceremonial blades
Marble	Metamorphosed limestone	3-4	2.7 g/cm3	Poorly defined	Irregular/splintery	Sculpture, architecture, lapidary
Granite	Mixture of minerals	6-7	2.65-2.8 g/cm3	Poorly defined	Irregular/splintery	Construction, sculpture, monuments
Sandstone	Quartz grains in matrix	4-6	2.2-2.8 g/cm3	None	Uneven	Construction, flooring, sculpture

Key points:

• Calcite is relatively soft with perfect cleavage, while other minerals like quartz and feldspar are much harder.
• Calcite has a low density compared to denser minerals like olivine.
• Marble is metamorphosed limestone so shares some similarities with calcite.
• Sandstone lacks cleavage planes found in calcite.
• The properties of calcite make it suitable for different uses than harder, tougher rocks.

Limestone and Travertine

Limestone is a sedimentary rock composed primarily of calcite and aragonite, along with other materials like clay, sand, or fossils. Travertine is a type of limestone formed by mineral springs, particularly hot springs. Both contain enough calcite to allow lapidarists to carve these into ornamental items. The presence of other minerals often creates decorative color patterns in the rock.

Properties of Calcite

Calcite has several unique properties that make it well-suited for lapidary work:

• Softness – With a Mohs hardness of 3, calcite is soft enough to be easily carved, sawed, and polished. This allows lapidarists to intricately shape it.
• Perfect Cleavage – The cleavage planes allow calcite to be split cleanly along smooth surfaces, helping reveal mesmerizing crystalline structures.
• Double Refraction – Iceland spar calcite demonstrates double refraction, separating light into two polarized rays. This unusual optical property creates a doubling effect.
• Fluorescence – Some calcite, like honey calcite, fluoresces under UV light, glowing green, yellow, orange, blue, pink or red. This adds visual interest.
• Solubility – Calcite’s solubility in acids allows lapidarists to use mild acids to selectively shape the material.
• Abundance – As a common mineral, calcite provides lapidarists with ample raw material to work with.

The combination of softness, cleavage, optical effects, fluorescence, solubility, and abundance make calcite a highly favorable material for creative lapidary applications.

Uses of Calcite in Lapidary Work

The ease of working with calcite enables lapidarists to transform it into diverse designs:

Jewelry Making

Although soft, calcite can be used to make pendants, beads, cameos, and other jewelry pieces. Care is required since calcite is fragile and sensitive to acids in skin oils and cleaners. It is best for occasional wear.

Carvings

Calcite’s softness allows detailed relief carvings depicting landscapes, animals, gods, skulls, or geometric patterns. Carvers use rotary tools, files, and abrasives to sculpt calcite.

Cabochons

Cabochons showcase the colorful patterns and crystals of calcite. Lapidarists expertly shape calcites into smooth domed cabochons using saws, grinders, and polishers.

Spheres

Calcite’s cleavage planes naturally form the crystal shape known as a rhombohedron, which resembles a sphere. When polished, they create stunning display spheres.

Eggs and Vases

The solubility of calcite enables lapidarists to use dilute acids to hollow out material and craft delicate decorative eggs, vases, and bowls.

Intarsia and Inlays

Intricate calcite inlays adorn boxes, furniture, walls, and other objects. Contrasting colors create eye-catching geometric designs.

Bookends and Objets D’art

Bookends and collectible lapidary objects can incorporate carved calcite and highlight its crystalline structures and hues. The varied crystal habits offer many possibilities.

With creativity and skill, lapidarists can fashion calcite into anything from jewelry and carvings to eggs and bookends. The softness and abundance of the material present almost limitless potential.

Types of Calcite Lapidary Work

Lapidarists employ an array of techniques when working with calcite:

Sculpting

Powerful Dremel or Foredom rotary tools with different bits allow lapidarists to abrade and sculpt calcite into intricate carvings. Needle files, wet sanding, and abrasives refine the details.

Cabochon

Cutting Cabochon cutting involves securing calcite on a dop stick using wax before shaping it on a lapidary wheel. Progressively finer grits are used to form the domed shape and polish the surface.

Carving

Jewelry engraving tools, small chisels, and micro motor engravers give lapidarists precision when hand carving designs into calcite. This direct carving method provides excellent control.

Tumbling

Small pieces of calcite can be tumbled with abrasive grit in a rotating drum lapidary tumbler to create polished beads and stones. Several stages progressively abrade and polish the material.

Grinding

For grinding and shaping, lapidarists turn to silicon carbide wheels or diamond-embedded wheels. Water prevents overheating. The grinding exposes the inner crystals.

Polishing

After coarse grinding, a series of polishing buffs affixed to the lapidary wheels smoothes calcite specimens to a glossy shine. The buffs use diamond or aluminum oxide polishing compounds.

Etching

Immersing carved calcite in dilute acid creates interesting etched effects. The acid dissolves certain spots on the surface depending on the exposure. Rinsing stops the reaction.

The array of lapidary techniques allows calcite to be fashioned into anything imaginable. While challenging due to fragility, calcite rewards lapidarists with stunning results.

Challenges Working with Calcite

Despite its allure, calcite poses some challenges for lapidarists:

• Fragility – The softness and perfect cleavage of calcite make it prone to chipping, cracking, and breaking if handled improperly. Extra care and precision are required.
• Acid Reactivity -Calcite readily reacts with acids, including skin oils. It requires occasional re-polishing and is unsuitable for acidic wearers. Careful handling prevents damage.
• Refractive Inclusions – Transparent specimens may contain dual inclusions that can double, blurring designs. Inclusions should be avoided.
• Incomplete Crystallization – Some calcite forms poorly defined crystals with hollow spots and zoning. Lapidarists select only the highest quality material.
• UV Damage – Prolonged UV exposure can diminish fluorescence and alter the color. Calcite jewelry should be stored away from light.

While demanding to work with, these challenges can be mitigated by an experienced lapidary artist. The rewards of transforming calcite into remarkable designs makes the effort worthwhile.

Popular Uses of Calcite

Beyond lapidary work, calcite has many popular applications:

• Construction – Calcite as limestone and marble creates strong yet attractive concrete, cement, tiles, and dimension stone for buildings and monuments.
• Agriculture – Crushed limestone balances soil acidity. Calcite also provides calcium, an essential plant nutrient.
• Medicine – Antacids like Tums contain calcium carbonate from calcite to neutralize stomach acid and treat heartburn.
• Paper – Calcite gives paper brightness, smoothness, and opacity. It also controls acidity during paper processing.
• Optics – Iceland spar was used in optical equipment due to its double refraction properties. It split light into polarized rays.
• Paint – As an inexpensive white pigment, ground calcite provides color, luster, and body in paint. It also resists corrosion.
• Plastics and Rubber – Calcite is used as an inexpensive filler and stiffener in plastic and rubber products. It improves strength.

The properties that make calcite useful for lapidary also provide benefits in its many industrial applications, demonstrating the diverse capabilities of the mineral.

FAQ

What is calcite?

Calcite is a common mineral composed of calcium carbonate (CaCO3). It is a major component of sedimentary rocks like limestone and metamorphic rocks like marble.

What is calcite used for?

Calcite has many uses, especially in construction materials like cement, concrete, statues and benches. It is also used in antacids, animal feeds, whitening paints and some believe it has spiritual cleansing properties.

What is the hardness of calcite?

Calcite has a hardness of 3 on the Mohs hardness scale, so it is relatively soft. Glass has a hardness of 5.5-7, so glass can scratch calcite.

Does calcite fluoresce?

Yes, calcite exhibits fluorescence under UV light, glowing in colors like white, green, blue, red, orange and pink. This makes it popular for mineral collectors.

How does calcite differ from quartz?

Calcite is a carbonate while quartz is a silicate. Also, quartz has a hardness of 7 on Mohs scale, much harder than calcite’s 3.

Where is calcite found?

Calcite is found all over the world in sedimentary, metamorphic and igneous rocks. It often fills spaces and cracks in other rocks.

Concluding Thoughts

With its stunning crystal forms, dazzling colors, and myriad varieties, it is no wonder calcite has been prized by lapidarists for centuries. Calcite’s softness allows it to be readily carved and polished into jewelry, carvings, cabochons, eggs, and objets d’art, while its abundance ensures lapidarists have ample material to work with. Challenges like fragility and acid reactivity mean lapidarists must handle calcite with care and precision. However, the results of transforming calcite into lapidary creations is rewarding. There are few other minerals that offer lapidarists the same versatility, artistry, and abundant raw materials as calcite. The beauty and variety calcite provides continues to inspire lapidarists’ creative pursuits.