Mama's Weekly Rock Facts

AMMONITE

Ammonites are extinct cephalopods (class Cephalopoda) as are the modern-day squid, octopus, and nautilus.  Various types of Ammonites lived over a long time range, 400 to 65 million years ago, and therefore have a relatively large amount of orders and suborders, which means there are a lot different types of Ammonite fossils available.

Ammonite septa & chambers

It is believed that the age of an Ammonite at death is estimated from the number of septa it has.  Septa are the dividing walls between the chambers of the shell.   The septa along with the suture (where the septa joins the outer wall) and the siphuncles (tubular outer rim connecting the chambers) determine the orders and species.  

Ammonites are named for their spiral shaped shells, which resemble the ram’s horns of the Egyptian god Amun.





by Amanda Rice, Resident Geologist, Mama's Minerals 

Mama's Weekly Rock Facts - KNIGHTIA FISH

KNIGHTIA FISH

Knightia Fish Plaques starting at $13.99

Knightia fish (Knightia eocaena) belong to the family Clupeidae, which includes herring and sardines.  Found in large quantities in the lacustrine sediments of what is now known as the Green River Formation, Knightia fish are well-preserved due to a slowed decomposition with the lack of oxygen at the cold lake bottoms. 

The green river formation is a group of sedimentation records from multiple intermountain lakes in three basins around what is now the Green River in Wyoming, Utah, and Colorado, USA.   One of the best know fossil locations is Fossil Butte National Monument, which is part of the Fossil Lake Formation and highly prized for the abundance of well-preserved fossils.

These small schooling fish rarely reach 10 inches in length and ate mainly plankton and diatoms, but were a good food source for larger predators of the Eocene epoch, lasting approximately 56 to 34 million years ago.
By Amanda Rice

Mama's Weekly Rock Facts - Ammolite

Ammolite is gemstone quality fossilized ammonite shells usually placenticeras meeki or placenticeras intercalare species.   Ammolite is a thin and fragile sheet of fossilized material most commonly in Reds and greens because of fragility of other colors such as purples, blues, and yellows.  These later colors are considered rarer and are more desirable as a gemstone.

The stacking layers of aragonite, which causes light interference, create the iridescent play of colors.  The crackling effect is cause by exposure to the elements and sediment compression where the thin Ammolite cracks and flakes.  This crackling appearance leads to the nickname ‘dragon skin’ for its scale like patterns.

Gem quality Ammolite is primarily found along the eastern front of North Americas Rocky Mountains, from Alberta Canada and south to Idaho / Montana in the United States.  Native American tribes in this region have long prized Ammolite.  The Blackfeet tribe call Ammolite “buffalo stone” and believe the amuletic stone aids in hunting buffalo and possesses healing powers.

Mineralogy: 

Ammolite: CaCo₃, aragonite polymorph with small impurities of calcite, pyrite, silica, and others

Mohs scale hardness: 4.5 - 5.5

Luster: greasy to dull

Color: gray to brown matrix with primarily red to green iridescence

Transparency: Opaque

Fracture: Uneven to granular

Specific gravity: 2.60 – 2.85

Index of refraction: 1.52 – 1.68

Cleavage: no true cleavage

Metaphysical Properties:

Stone of luck, general healing; detoxify the body, and improve energy flow

Image from Wikipedia

by Amanda Rice