Carve some ASCII jewels! March 13 is recognized as National Jewel Day, which is the theme of this challenge. So, given an integer n where n is greater than 0, create an ASCII jewel. For example:

n = 1          n = 2             n = 3
                                       ______
                     ____             /      \
 __                 /    \            \      /
/  \                \    /             \    /
\  /                 \  /               \  /
 \/                   \/                 \/


The bottom is defined as the very bottom of the jewel to the highest pair of of \/. The rest is the top. For the above example where n = 1:

Bottom: \  /    Top:   __
         \/           /  \


As you can see, the bottom is made of n + 1 layers of \/ with (1 * lines from the bottom) * 2 spaces in between with a maximum of n lines from the bottom of the jewel. If we take the second jewel (n = 2), we can see that:

 ____
/    \      
\    /  2 (or n) layers from the bottom with 1*2*2 or 4 spaces in between \/
 \  /   1 layer from the bottom with 1*1*2 or 2 spaces in between \/
  \/    The bottom (0 layers) with 1*0*2 spaces or 0 spaces in between \/


The top is made of one pair of /\ with n*2 spaces in between with n*2 underscores on top.

Rules


Must be able to take in any nonzero positive integers as user input
Must create a jewel with the specs defined above (restated here):


The top is made of one pair of /\ with n*2 spaces in between with n*2 underscores on top.
The bottom is made of n + 1 layers of \/ with (1 * lines from the bottom) * 2 spaces in between with a maximum of n lines from the bottom of the jewel.

Trailing newlines after the jewel, or trailing spaces on each line are allowed.
No standard loopholes allowed


Winning Criteria

Least bytes wins!
Charcoal, 17 bytes

Code:

ＮβＧ←β_↙↙¹→↘⁺β¹‖Ｍ→


Explanation:

Ｎβ                      # Place the input into β
   Ｇ←β_                 # Draw a line of length β with _ as the filling character
        ↙                # Move the cursor one down and one left
         ↙¹              # Draw a line from the cursor position to one position ↙
           →             # Move the cursor 1 to the right
             ⁺β¹         # Add one to the input and..
            ↘            # Create a line pointing ↘, with the size calculated above
                ‖Ｍ→     # Mirror to the right


A very neat command is ‖Ｍ, which also automatically mirrors / into \.

Uses the Charcoal encoding. 

Try it online!