ICELAND SPAR: THROUGH THE LOOKING-GLASS
Rock&Gem Magazine|April 2023
In Through the Looking-Glass, the sequel to Alice's Adventures in Wonderland, author Lewis Carroll used the title phrase as a metaphor for peering into a world where nothing was quite what it seemed. When it came to understanding the mysterious nature of light, the "looking glass" for early scientists was optical calcite or Iceland spar.
STEVE VOYNICK
ICELAND SPAR: THROUGH THE LOOKING-GLASS

Specimens of the Iceland spar variety of calcite are popular items in rock shops and at gem-and-mineral shows. Looking like miniature ice cubes, these colorless, transparent, cleaved rhombohedrons sell for only a few dollars each. But the commonplaceness of these little rhombohedrons belies a fascinating history that has a profound impact on science and technology.

Calcite (calcium carbonate, CaCO3) crystallizes in the trigonal system and is slightly denser than quartz. Pure calcite is colorless, but impurities impart a range of soft colors. With its weak ionic bonding, calcite is rather soft (Mohs 3.0) and cleaves easily into rhombohedrons.

Birefringence is calcite's most notable property. This ability to polarize light and refract it in two slightly different directions creates the double images seen when objects are viewed through Iceland spar crystals.

SUN STONE

Centuries before the magnetic compass was introduced to Europe, Viking mariners were demonstrating an uncanny ability to navigate the northern seas, even when cloudiness and fog obscured the sun or when the sun was below the horizon.

Icelandic monastery texts dating to 1250 mention a sólarsteinn (sun stone) that the Vikings used to determine the sun's position without direct solar sightings. When a sun stone was held against the eye while scanning the horizon, polarized light cast two shadowy images upon the retina. The horizontal deflection at which their darkness equalized accurately indicated the position of the unseen sun.

This story is from the {{IssueName}} edition of {{MagazineName}}.

Start your 7-day Magzter GOLD free trial to access thousands of curated premium stories, and 9,000+ magazines and newspapers.

This story is from the {{IssueName}} edition of {{MagazineName}}.

Start your 7-day Magzter GOLD free trial to access thousands of curated premium stories, and 9,000+ magazines and newspapers.

MORE STORIES FROM ROCK&GEM MAGAZINEView all
This News is for the Birds
Rock&Gem Magazine

This News is for the Birds

The amazing range of the would-be birds!

time-read
1 min  |
July 2024
CALIFORNIA MAGNESITE PLASMA AGATE
Rock&Gem Magazine

CALIFORNIA MAGNESITE PLASMA AGATE

California magnesite plasma agate is a kaleidoscope of minerals. Much like its neighbor from Clear Creek, it contains chalcedony, serpentine, jadeite and chromite.

time-read
3 mins  |
July 2024
HOW TO CREATE A CABBING MATERIAL
Rock&Gem Magazine

HOW TO CREATE A CABBING MATERIAL

Even though Mother Nature creates almost unbounded types and numbers of beautiful materials for cabbing, often I struggle to find a slab that will work for the project that I want to do.

time-read
2 mins  |
July 2024
PINWHEEL - VIET GEMS 149
Rock&Gem Magazine

PINWHEEL - VIET GEMS 149

I am frequently asked what my favorite gemstone designs are and where to find them. After my trip to the Tucson Gem and Mineral Show, I updated my list of favorites to include gemstone designer, Phan Thanh Trung.

time-read
1 min  |
July 2024
Copper Minerals: My Favorite
Rock&Gem Magazine

Copper Minerals: My Favorite

I have lived in the “Copper State” of Arizona for 65 years so it should not surprise readers that copper minerals are among my favorites to collect.

time-read
4 mins  |
July 2024
OPPENHEIMER, TRINITY SITE AND TRINITITE
Rock&Gem Magazine

OPPENHEIMER, TRINITY SITE AND TRINITITE

The widely acclaimed, 2023 Hollywood biographical movie Oppenheimer recently won seven Academy Awards including Best Picture and Best Actor (Cillian Murphy).

time-read
3 mins  |
July 2024
Clearing ,Smudging & Setting Intentions for Stones
Rock&Gem Magazine

Clearing ,Smudging & Setting Intentions for Stones

Why do you believe what you believe? Are your beliefs true because you choose to believe them? Whether it is religion, science or the metaphysical, your belief and faith make it real to you in mind, body and soul.

time-read
7 mins  |
July 2024
Rhode Island's Hobbit Stone Age
Rock&Gem Magazine

Rhode Island's Hobbit Stone Age

Rhode Island may be 22nd out of 30 states in miles of total coastline but when you compare coastline length to land acres, it ranks second only to Maryland.

time-read
4 mins  |
July 2024
Black Range Amethyst
Rock&Gem Magazine

Black Range Amethyst

Amethyst in Southwest New Mexico

time-read
7 mins  |
July 2024
EQUINE Bling!
Rock&Gem Magazine

EQUINE Bling!

How an Oklahoma Saddle Maker Uses Moissanite, Gold, Silver Turquoise tc to Adorn Saddles Jewelry

time-read
4 mins  |
July 2024