Carbon APEX Mineral

Carbon (C #6) is the next element on the periodic table for my APEX mineral collection.  
Wikipedia Carbon

Carbon Minerals - more minerals than any other element.

My APEX Carbon mineral can be pure graphite with 100% Carbon.  Diamond would be the prettiest but I don't think a nice visible sample for my cabinet would be cost effective.  For that reason I choose the Graphite allotrope.  Organic coal deposits can actually morph into graphite deposits through geologic processes.  I have to be careful with my mineral sample since this stuff is so soft that it just rubs off on everything. 

Carbon is the fourth most abundant chemical element in the universe by mass after hydrogen, helium, and oxygen.    

There are several allotropes of Carbon with the best known being graphite and diamond.  What is interesting is that these have completely opposite properties in some ways.

• Diamond is highly transparent, while graphite is opaque and black.
• Diamond is among the hardest materials known, while graphite is soft enough to form a streak on paper.
• Diamond has a very low electrical conductivity, while graphite is a very good conductor. 

Carbon is normally either solid or gas.  Even the most basic properties of liquid Carbon have long been debated because of the challenge of studying the material at the required temperatures and pressures.  

Only Carbon and a few metals remain solid at 5000 degrees Kelvin.

Carbon was discovered in prehistory and was known in the forms of soot and charcoal to the earliest human civilizations. Diamonds were known probably as early as 2500 BCE in China, while carbon in the form of charcoal was made around Roman times by the same chemistry as it is today, by heating wood in a pyramid covered with clay to exclude air.[

The major economic use of carbon other than food and wood is in the form of hydrocarbons.

Carbon is critical to life on Earth.  DNA, Proteins, and all organic compounds contain Carbon in some form.  Hydrocarbon deposits are most certainly some form of decayed living organisms.  Whether this deposition process occurs at the crustal surface on Earth or deep within the Earth are up for debate.