Why Doesn't the Z axis exist for the mouse, and is there way to get the Z axis?

I'm making a while loop that will move the part to the mouse always, so I can create a building system.

--Variables
local player = game.Players.LocalPlayer
local mouse = player:GetMouse()
local Part = game.Workspace.Farm:Clone()
Part.Parent = game.Workspace
--Move Part to Mouse Position Always
while true do
        local x = mouse.X
        local y = mouse.Y
        Part.Position = Vector3.new(x,y)

--Places Part at Mouse Position.
    mouse.Button1Down:connect(function(hit)
        local X = mouse.hit.X
        local Y = mouse.hit.Y
        local Z = mouse.hit.Z
        local Partt = Part:Clone()
        Partt.Parent = game.Workspace
        Partt.Anchored = true
        Partt.Position = Vector3.new(X,Y,Z)
        wait(5)
        Partt:Destroy()
    end)
    wait()
end