Femic Minerals (mafic minerals)

Question 1

femic minerals are

Answer 1

• 𝐃𝐚𝐫𝐤 𝐦𝐢𝐧𝐞𝐫𝐚𝐥𝐬 with a 𝐡𝐢𝐠𝐡 𝐝𝐞𝐧𝐬𝐢𝐭𝐲.
• 𝐌𝐚𝐠𝐧𝐞𝐬𝐢𝐮𝐦 and 𝐈𝐫𝐨𝐧 are usually prominent
• 𝐝𝐞𝐧𝐬𝐢𝐭𝐲: 3,2 - 3,6
• Typical 𝐦𝐢𝐧𝐞𝐫𝐚𝐥 𝐟𝐚𝐦𝐢𝐥𝐢𝐞𝐬 are:
  1. Pyroxenes
  2. Amphiboles
  3. Micas
  4. Ca-Feldspars
  5. Olivines

Question 2

Micas

Answer 2

• essentially 𝐡𝐲𝐝𝐫𝐚𝐭𝐞𝐝 𝐩𝐨𝐭𝐚𝐬𝐬𝐢𝐮𝐦, 𝐬𝐨𝐝𝐢𝐮𝐦 or 𝐥𝐢𝐭𝐡𝐢𝐮𝐦 𝐚𝐥𝐮𝐦𝐢𝐧𝐢𝐮𝐦 silicates
• minerals with perfect 𝐛𝐚𝐬𝐚𝐥 𝐜𝐥𝐞𝐚𝐯𝐚𝐠𝐞 and 𝐡𝐢𝐠𝐡 𝐥𝐮𝐬𝐭𝐫𝐞
• most important are:
  1. 𝐌𝐮𝐬𝐜𝐨𝐯𝐢𝐭𝐞 (white mica)
  2. 𝐁𝐢𝐨𝐭𝐢𝐭𝐞 (black mica)
  3. 𝐏𝐡𝐥𝐨𝐠𝐨𝐩𝐢𝐭𝐞 (brown mica)
• 𝐌𝐮𝐬𝐜𝐨𝐯𝐢𝐭𝐞 and 𝐁𝐢𝐨𝐭𝐢𝐭𝐞 are common in 𝐢𝐠𝐧𝐞𝐨𝐮𝐬 and 𝐦𝐞𝐭𝐚𝐦𝐨𝐫𝐩𝐡𝐢𝐜 rocks
• 𝐏𝐡𝐥𝐨𝐠𝐨𝐩𝐢𝐭𝐞 is typical of 𝐮𝐥𝐭𝐫𝐚𝐛𝐚𝐬𝐢𝐜 𝐢𝐠𝐧𝐞𝐨𝐮𝐬 rocks

Question 3

Pyroxenes

Answer 3

*divided into two types; -

         1. those that crystallise in the monoclinic crystal 
         system (𝐜𝐥𝐢𝐧𝐨𝐩𝐲𝐫𝐨𝐱𝐞𝐧𝐞𝐬) 

         2. those that crystallise in the orthorhombic 
         system (𝐨𝐫𝐭𝐡𝐨𝐩𝐲𝐫𝐨𝐱𝐞𝐧𝐞𝐬)

• two 𝐩𝐫𝐢𝐬𝐦𝐚𝐭𝐢𝐜 𝐜𝐥𝐞𝐚𝐯𝐚𝐠𝐞𝐬 that intersect at nearly 𝟗𝟎𝐨
• common in 𝐛𝐚𝐬𝐢𝐜 𝐢𝐠𝐧𝐞𝐨𝐮𝐬 rocks
• most important 𝐜𝐥𝐢𝐧𝐨𝐩𝐲𝐫𝐨𝐱𝐞𝐧𝐞𝐬 are:
  1. 𝐚𝐮𝐠𝐢𝐭𝐞 which is black or dark brown
  2. green 𝐝𝐢𝐨𝐩𝐬𝐢𝐝𝐞
• 𝐨𝐫𝐭𝐡𝐨𝐩𝐲𝐫𝐨𝐱𝐞𝐧𝐞𝐬 include:
  1. 𝐞𝐧𝐬𝐭𝐚𝐭𝐢𝐭𝐞
  2. 𝐡𝐲𝐩𝐞𝐫𝐬𝐭𝐡𝐞𝐧𝐞

Question 4

Amphiboles

Answer 4

• 𝐬𝐢𝐦𝐢𝐥𝐚𝐫 𝐭𝐨 𝐩𝐲𝐫𝐨𝐱𝐞𝐧𝐞𝐬 in composition but are 𝐡𝐲𝐝𝐫𝐨𝐮𝐬 (with H2O)
• crystallise in the 𝐦𝐨𝐧𝐨𝐜𝐥𝐢𝐧𝐢𝐜 system.
• two 𝐩𝐫𝐢𝐬𝐦𝐚𝐭𝐢𝐜 𝐜𝐥𝐞𝐚𝐯𝐚𝐠𝐞𝐬 that intersect at nearly 𝟔𝟎𝐨.
• 𝐇𝐨𝐫𝐧𝐛𝐥𝐞𝐧𝐝𝐞 is the most important and is similar to 𝐚𝐮𝐠𝐢𝐭𝐞 in composition and is black or greenish-black.
• 𝐀𝐦𝐩𝐡𝐢𝐛𝐨𝐥𝐞𝐬 are common in both 𝐢𝐠𝐧𝐞𝐨𝐮𝐬 and 𝐦𝐞𝐭𝐚𝐦𝐨𝐫𝐩𝐡𝐢𝐜 rocks.

Question 5

Olivines

Answer 5

• yellow-green to brownish
• has a density of 3,3 to 3,5.
• Its composition varies depending on the relative quantity of Mg to Fe.
• Olivine is typical of so-called ultrabasic rocks