Salic Minerals (felsic minerals)

Question 1

what are Salic Minerals?

Answer 1

• 𝐋𝐢𝐠𝐡𝐭/𝐜𝐨𝐥𝐨𝐫𝐥𝐞𝐬𝐬 minerals with a 𝐥𝐨𝐰 𝐝𝐞𝐧𝐬𝐢𝐭𝐲.
• 𝐬𝐢𝐥𝐢𝐜𝐚 (𝐪𝐮𝐚𝐫𝐭𝐳) and 𝐚𝐥𝐮𝐦𝐢𝐧𝐢𝐮𝐦 𝐬𝐢𝐥𝐢𝐜𝐚𝐭𝐞𝐬 are prominent
• 𝐝𝐞𝐧𝐬𝐢𝐭𝐲 = 2,7
• Typical 𝐦𝐢𝐧𝐞𝐫𝐚𝐥 𝐟𝐚𝐦𝐢𝐥𝐢𝐞𝐬 are:
  
  1. Quartz
  2. Feldspars
  3. Feldspathoids

these minerals are abundant in 𝐚𝐜𝐢𝐝𝐢𝐜 𝐢𝐠𝐧𝐞𝐨𝐮𝐬 𝐫𝐨𝐜𝐤𝐬

Question 2

Quartz

Answer 2

𝐐𝐮𝐚𝐫𝐭𝐳 is a glassy mineral that has a characteristic conchoidal fracture and a hardness of 7. It is common in acid igneous, sedimentary and metamorphic rocks.

Question 3

Feldspars

Answer 3

Feldspars are probably the most common of the minerals. this group includes:

• 𝐩𝐨𝐭𝐚𝐬𝐡 𝐟𝐞𝐥𝐝𝐬𝐩𝐚𝐫𝐬 {K2O.A12O3.6SiO2} (potassium aluminium silicate) This composition crystallises as 𝐨𝐫𝐭𝐡𝐨𝐜𝐥𝐚𝐬𝐞 or 𝐦𝐢𝐜𝐫𝐨𝐜𝐥𝐢𝐧𝐞. Both have a density slightly less than 2,6.
• 𝐬𝐨𝐝𝐚 𝐟𝐞𝐥𝐝𝐬𝐩𝐚𝐫 (composition Na2O.A12O3.6SiO2) is known as 𝐚𝐥𝐛𝐢𝐭𝐞
• 𝐥𝐢𝐦𝐞 𝐟𝐞𝐥𝐝𝐬𝐩𝐚𝐫 (composition CaO.A12O3.2SiO2) is known as 𝐚𝐧𝐨𝐫𝐭𝐡𝐢𝐭𝐞
• 𝐚𝐥𝐛𝐢𝐭𝐞 and 𝐚𝐧𝐨𝐫𝐭𝐡𝐢𝐭𝐞 form an 𝐢𝐬𝐨𝐦𝐨𝐫𝐩𝐡𝐨𝐮𝐬 𝐬𝐞𝐫𝐢𝐞𝐬 known as 𝐩𝐥𝐚𝐠𝐢𝐨𝐜𝐥𝐚𝐬𝐞 and is 𝘤𝘰𝘭𝘰𝘶𝘳𝘭𝘦𝘴𝘴, 𝘸𝘩𝘪𝘵𝘦, 𝘨𝘳𝘦𝘺 𝘰𝘳 𝘺𝘦𝘭𝘭𝘰𝘸𝘪𝘴𝘩 with two cleavages and density varies from 2,6 to 2,8.

Question 4

Feldspathoids

Answer 4

somewhat similar to the feldspars in composition but with a much lower 𝐬𝐢𝐥𝐢𝐜𝐚 (𝐒𝐢𝐎𝟐) content. They are much less common and occur in so-called undersaturated (with respect to silica) rocks.

• 𝐥𝐞𝐮𝐜𝐢𝐭𝐞 with the composition K2O.A12O3.4SiO2
• 𝐧𝐞𝐩𝐡𝐞𝐥𝐢𝐧𝐞 with the composition Na2O.A12O3.2SiO2.